| 1. |
- Ahlm, Lars, 1976-, et al.
(författare)
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A comparison of dry and wet season aerosol number fluxes over the Amazon rain forest
- 2010
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 10:6, s. 3063-3079
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Tidskriftsartikel (refereegranskat)abstract
- Vertical number fluxes of aerosol particles and vertical fluxes of CO2 were measured with the eddy covariance method at the top of a 53m high tower in the Amazon rain forest as part of the LBA (The Large Scale Biosphere Atmosphere Experiment in Amazonia) experiment. The observed aerosol number fluxes included particles with sizes down to 10 nm in diameter. The measurements were carried out during the wet and dry season in 2008. In this study focus is on the dry season aerosol fluxes, with significant influence from biomass burning, and these are compared with aerosol fluxes measured during the wet season. Net particle deposition fluxes dominated in daytime in both seasons and the deposition flux was considerably larger in the dry season due to the much higher dry season particle concentration. The particle transfer velocity increased linearly with increasing friction velocity in both seasons. The difference in transfer velocity between the two seasons was small, indicating that the seasonal change in aerosol number size distribution is not enough for causing any significant change in deposition velocity. In general, particle transfer velocities in this study are low compared to studies over boreal forests. The reasons are probably the high percentage of accumulation mode particles and the low percentage of nucleation mode particles in the Amazon boundary layer, both in the dry and wet season, and low wind speeds in the tropics compared to the midlatitudes. In the dry season, nocturnal particle fluxes behaved very similar to the nocturnal CO2 fluxes. Throughout the night, the measured particle flux at the top of the tower was close to zero, but early in the morning there was an upward particle flux peak that is not likely a result of entrainment or local pollution. It is possible that these morning upward particle fluxes are associated with emission of primary biogenic particles from the rain forest. Emitted particles may be stored within the canopy during stable conditions at nighttime, similarly to CO2, and being released from the canopy when conditions become more turbulent in the morning.
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| 2. |
- Ahlm, Lars, 1976-, et al.
(författare)
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Aerosol number fluxes over the Amazon rain forest during the wet season
- 2009
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Ingår i: Atmospheric Chemistry And Physics. - 1680-7316 .- 1680-7324. ; 9:24, s. 9381-9400
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Tidskriftsartikel (refereegranskat)abstract
- Number fluxes of particles with diameter larger than 10 nm were measured with the eddy covariance method over the Amazon rain forest during the wet season as part of the LBA (The Large Scale Biosphere Atmosphere Experiment in Amazonia) campaign 2008. The primary goal was to investigate whether sources or sinks dominate the aerosol number flux in the tropical rain forest-atmosphere system. During the measurement campaign, from 12 March to 18 May, 60% of the particle fluxes pointed downward, which is a similar fraction to what has been observed over boreal forests. The net deposition flux prevailed even in the absolute cleanest atmospheric conditions during the campaign and therefore cannot be explained only by deposition of anthropogenic particles. The particle transfer velocity vt increased with increasing friction velocity and the relation is described by the equation vt=2.4×10−3×u* where u* is the friction velocity. Upward particle fluxes often appeared in the morning hours and seem to a large extent to be an effect of entrainment fluxes into a growing mixed layer rather than primary aerosol emission. In general, the number source of primary aerosol particles within the footprint area of the measurements was small, possibly because the measured particle number fluxes reflect mostly particles less than approximately 200 nm. This is an indication that the contribution of primary biogenic aerosol particles to the aerosol population in the Amazon boundary layer may be low in terms of number concentrations. However, the possibility of horizontal variations in primary aerosol emission over the Amazon rain forest cannot be ruled out.
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| 3. |
- Ahlm, Lars, et al.
(författare)
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Emission and dry deposition of accumulation mode particles in the Amazon Basin
- 2010
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 10:21, s. 10237-10253
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Tidskriftsartikel (refereegranskat)abstract
- Size-resolved vertical aerosol number fluxes of particles in the diameter range 0.25–2.5 μm were measured with the eddy covariance method from a 53 m high tower over the Amazon rain forest, 60 km NNW of Manaus, Brazil. This study focuses on data measured during the relatively clean wet season, but a shorter measurement period from the more polluted dry season is used as a comparison. Size-resolved net particle fluxes of the five lowest size bins, representing 0.25–0.45 μm in diameter, pointed downward in more or less all wind sectors in the wet season. This is an indication that the source of primary biogenic aerosol particles may be small in this particle size range. In the diameter range 0.5–2.5 μm, vertical particle fluxes were highly dependent on wind direction. In wind sectors where anthropogenic influence was low, net emission fluxes dominated. However, in wind sectors associated with higher anthropogenic influence, net deposition fluxes dominated. The net emission fluxes were interpreted as primary biogenic aerosol emission, but deposition of anthropogenic particles seems to have masked this emission in wind sectors with higher anthropogenic influence. The emission fluxes were at maximum in the afternoon when the mixed layer is well developed, and these emissions were best correlated with horizontal wind speed by the equation log10F=0.47·U+2.26 where F is the emission number flux of 0.5–2.5 μm particles [m−2s−1] and U is the horizontal wind speed [ms−1] at the top of the tower.
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| 5. |
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| 6. |
- Dencker, Kerstin, 1972-
(författare)
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An Analysis of the Proactive Approach as a Potential Tool for Adaptability in Production Systems
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Competitive systems for manufacturing, especially assembly systems, have to cope with frequent changes of external as well as internal demands. A proactive behaviour in an assembly system should make it capable of rapid changes and have an ability to handle frequent changes and disturbances. During recent decades several different system theories have occurred of which the majority remained theories never taken to actual production solutions. The thesis presents results from four case studies. It is suggested, that the proactivity of an assembly system is strongly influenced by the system’s ability to change the three parameters: 1) level of automation, 2) level of information, 3) level of competence[l3] (among the operators in a defined work area). Proactivity is not easy to describe. However, this[l4] thesis has taken a step in that direction. A general definition of proactivity is “taking action by causing change towards a state and not only reacting to change when it happens”. Another way to phrase this is "to be anticipatory and taking charge of situations”. Proactivity can be described as the ability of preparation for: - Changes and disturbance during operation; - Planned long-term evolution for a sustainable and perfect production system. Such a system consists of technical components efficiently integrated with human operators and has the ability to handle frequent changes. Proactivity in an assembly system is dependent on the following factors: - Continuous changes; - Mandate to allocate resources; - Mandate to do short term planning. The thesis presents a first model for evaluation of different technical resources that contributes to an overall proactive system behaviour. The model has been published but not yet tested.
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| 7. |
- Endres, Sonja, et al.
(författare)
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A New Perspective at the Ship-Air-Sea-Interface : The Environmental Impacts of Exhaust Gas Scrubber Discharge
- 2018
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Ingår i: Frontiers in Marine Science. - : FRONTIERS MEDIA SA. - 2296-7745. ; 5
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Forskningsöversikt (refereegranskat)abstract
- Shipping emissions are likely to increase significantly in the coming decades, alongside increasing emphasis on the sustainability and environmental impacts of the maritime transport sector. Exhaust gas cleaning systems ("scrubbers"), using seawater or fresh water as cleaning media for sulfur dioxide, are progressively used by shipping companies to comply with emissions regulations. Little is known about the chemical composition of the scrubber effluent and its ecological consequences for marine life and biogeochemical processes. If scrubbers become a central tool for atmospheric pollution reduction from shipping, modeling, and experimental studies will be necessary to determine the ecological and biogeochemical effects of scrubber wash water discharge on the marine environment. Furthermore, attention must be paid to the regulation and enforcement of environmental protection standards concerning scrubber use. Close collaboration between natural scientists and social scientists is crucial for progress toward sustainable shipping and protection of the marine environment.
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| 8. |
- Fahlgren, Camilla, et al.
(författare)
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Seawater mesocosm experiments in the Arctic uncover differential transfer of marine bacteria to aerosols
- 2015
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Ingår i: Environmental Microbiology Reports. - : Wiley. - 1758-2229 .- 1758-2229. ; 7:3, s. 460-470
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Tidskriftsartikel (refereegranskat)abstract
- Biogenic aerosols critically control atmospheric processes. However, although bacteria constitute major portions of living matter in seawater, bacterial aerosolization from oceanic surface layers remains poorly understood. We analysed bacterial diversity in seawater and experimentally generated aerosols from three Kongsfjorden sites, Svalbard. Construction of 16S rRNA gene clone libraries from paired seawater and aerosol samples resulted in 1294 sequences clustering into 149 bacterial and 34 phytoplankton operational taxonomic units (OTUs). Bacterial communities in aerosols differed greatly from correspondingseawater communities in three out of four experiments. Dominant populations of both seawater and aerosols were Flavobacteriia, Alphaproteobacteria and Gammaproteobacteria. Across the entire dataset, most OTUs from seawater could also be found in aerosols; in each experiment, however, several OTUs were either selectively enriched in aerosols or little aerosolized. Notably, a SAR11 clade OTU was consistently abundant in the seawater, but was recorded insignificantly lower proportions in aerosols. A strikingly high proportion of colony-forming bacteria were pigmented in aerosols compared with seawater, suggesting that selection during aerosolization contributes to explaining elevated proportions of pigmented bacteria frequently observed in atmospheric samples. Our findings imply that atmospheric processes could be considerably influenced by spatiotemporal variations in the aerosolization efficiency of different marine bacteria.
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| 9. |
- Hasan, Baha, 1977-
(författare)
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An Ontological Approach to support Knowledge Sharing between Product Design and Assembly Process Planning (APP)
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Modern manufacturing organizations have to cope with several critical issues arising from the need for mass customization such as short product life-cycles, an increasing number of product variants and frequently changing customer requirements. One of the main factors that could aid overcoming those challenges is the use of information and communication technology (ICT) applications over a collaborative manufacturing environment, in which all stakeholders share and exchange knowledge across different manufacturing domains and applications. However, the use of ICT applications over a collaborative manufacturing environment is limited at the domain level by semantic conflicts arising from the use of different ways to describe the same objects and facts arising from different conceptualizations. Similarly, ICT usage is limited on the application level by interoperability problems arising from diverse heterogeneity between different ICT applications and tools.This research presents a semantic approach to support knowledge sharing within the assembly domain. More specifically, this research is focusing on capturing and sharing assembly design knowledge and integrating the assembly design domain and the Assembly Process Planning (APP) domain. Assembly design and APP are very important engineering domains for successful manufacturing system design, which requires an efficient collaborative environment for best utilization of the assembly resources. However, though these domains represent different perspectives in understanding of the same concepts, both domains use different software applications, which might cause interoperability issues.In this thesis, a novel integration approach has been proposed; this approach is composed of two stages: the first stage includes modelling and recognition of assembly knowledge semantics from SolidWorks (SW) CAD software by using SolidWorks’ Application Programmable Interface (SW-API). The second stage includes sharing the recognized assembly knowledge semantics by using a knowledge-based system in the form of a three-layer ontology architecture which provides a common semantic base to support knowledge sharing across assembly design and APP both on the domain and the application level. Each ontology layer shares a set of concepts from the most generic level to the most specialized level. The foundation ontology layer represents the general key concepts in the assembly design and APP domains. More specialized assembly design concepts and APP concepts are represented both in the domain ontology layer, and the application ontology layer. In the latter, concepts related to SolidWorks CAD software and to assembly robotic devices are represented.
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| 10. |
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