| 1. |
- Horst, Axel, et al.
(författare)
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Compound-specific bromine isotope analysis of methyl bromide using gas chromatography hyphenated with inductively coupled plasma multiple-collector mass spectrometry
- 2011
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Ingår i: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 25:17, s. 2425-2432
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Tidskriftsartikel (refereegranskat)abstract
- Methyl bromide is the most important natural bromine contributor to stratospheric ozone depletion, yet there are still large uncertainties regarding quantification of its sources and sinks. The stable bromine isotope composition of CH(3)Br is potentially a powerful tool to apportion its sources and to study both its transport and its reactive fate. A novel compound-specific method to measure (81)Br/(79)Br isotope ratios in CH3Br using gas chromatography hyphenated with inductively coupled plasma multiple-collector mass spectrometry (GC/MCICPMS) was developed. Sample amounts of >40 ng could bemeasured with a precision of 0.1 parts per thousand (1 sigma, n=3). The method results are reproducible over the long term as shown with 36 analyses acquired over 3 months, yielding a standard deviation ( 1s) better than 0.4 parts per thousand. This new method demonstrates for the first time Br isotope ratio determination in gaseous brominated samples. It is three orders of magnitude more sensitive than previously existing isotope ratio mass spectrometry methods for Br isotope determination of other organobromines, thus allowing applications towards ambient atmospheric samples.
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| 2. |
- Abreu, P, et al.
(författare)
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Measurement of the strange quark forward-backward asymmetry around the Z(0) peak
- 2000
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Ingår i: EUROPEAN PHYSICAL JOURNAL C. - : SPRINGER VERLAG. - 1434-6044. ; 14:4, s. 613-631
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Tidskriftsartikel (refereegranskat)abstract
- A precise measurement of the strange quark forward-backward asymmetry used 3.2 M multihadronic events around the Z(0) peak collected by the DELPHI experiment from 1992 to 1995. The ring imaging Cherenkov detectors in the barrel and end-cap regions identif
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| 3. |
- Ahlberg, Erik, et al.
(författare)
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"Vi klimatforskare stödjer Greta och skolungdomarna"
- 2019
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Ingår i: Dagens nyheter (DN debatt). - 1101-2447.
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- DN DEBATT 15/3. Sedan industrialiseringens början har vi använt omkring fyra femtedelar av den mängd fossilt kol som får förbrännas för att vi ska klara Parisavtalet. Vi har bara en femtedel kvar och det är bråttom att kraftigt reducera utsläppen. Det har Greta Thunberg och de strejkande ungdomarna förstått. Därför stödjer vi deras krav, skriver 270 klimatforskare.
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| 4. |
- Andersson, August, et al.
(författare)
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(14)C-Based source assessment of soot aerosols in Stockholm and the Swedish EMEP-Aspvreten regional background site
- 2011
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Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310 .- 1873-2844. ; 45:1, s. 215-222
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Tidskriftsartikel (refereegranskat)abstract
- Combustion-derived soot or black carbon (BC) in the atmosphere has a strong influence on both climate and human health. In order to propose effective mitigation strategies for BC emissions it is of importance to investigate geographical distributions and seasonal variations of BC emission sources. Here, a radiocarbon methodology is used to distinguish between fossil fuel and biomass burning sources of soot carbon (SC). SC is isolated for subsequent off-line (14)C quantification with the chemothermal oxidation method at 375 degrees C (CTO-375 method), which reflects a recalcitrant portion of the BC continuum known to minimize inadvertent inclusion of any non-pyrogenic organic matter. Monitored wind directions largely excluded impact from the Stockholm metropolitan region at the EMEP-Aspvreten rural station 70 km to the south-west. Nevertheless, the Stockholm city and the rural stations yielded similar relative source contributions with fraction biomass (f(biomass)) for fall and winter periods in the range of one-third to half. Large temporal variations in (14)C-based source apportionment was noted for both the 6 week fall and the 4 month winter observations. The f(biomass) appeared to be related to the SC concentration suggesting that periods of elevated BC levels may be caused by increased wood fuel combustion. These results for the largest metropolitan area in Scandinavia combine with other recent (14)C-based studies of combustion-derived aerosol fractions to suggest that biofuel combustion is contributing a large portion of the BC load to the northern European atmosphere.
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| 5. |
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| 6. |
- Andersson, August
(författare)
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A Model for the Spectral Dependence of Aerosol Sunlight Absorption
- 2017
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Ingår i: ACS Earth and Space Chemistry. - : American Chemical Society (ACS). - 2472-3452. ; 1:9, s. 533-539
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Tidskriftsartikel (refereegranskat)abstract
- Sunlight-absorbing aerosols, e.g., black and brown carbon (BC and BrC), have a potentially large, but highly uncertain contribution to climate warming. The spectral dependence of the aerosol absorption in the visible and near-UV regime is almost universally well-described with a heuristic power law, where the exponent is termed the absorption Angstrom exponent. However, the 2 underlying physicochemical causes for this relation are unknown. Here, a model is presented that predicts the emergence of the power law spectral dependence and unifies the absorption behavior of BC and BrC. Building on the theory of light absorption in amorphous materials, the interaction between multiple functional groups upon absorption is predicted to be a key feature for this broad spectral dependence. This aerosol amorphous absorption model is in agreement with recent empirical findings and provides a conceptual basis for the additional research needed to better constrain the optical properties of light-absorbing aerosols and their environmental impact.
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| 7. |
- Andersson, August
(författare)
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A systematic examination of a random sampling strategy for source apportionment calculations
- 2011
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 412, s. 232-238
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Tidskriftsartikel (refereegranskat)abstract
- Estimating the relative contributions from multiple potential sources of a specific component in a mixed environmental matrix is a general challenge in diverse fields such as atmospheric, environmental and earth sciences. Perhaps the most common strategy for tackling such problems is by setting up a system of linear equations for the fractional influence of different sources. Even though an algebraic solution of this approach is possible for the common situation with N + 1 sources and N source markers, such methodology introduces a bias, since it is implicitly assumed that the calculated fractions and the corresponding uncertainties are independent of the variability of the source distributions. Here, a random sampling (RS) strategy for accounting for such statistical bias is examined by investigating rationally designed synthetic data sets. This random sampling methodology is found to be robust and accurate with respect to reproducibility and predictability. This method is also compared to a numerical integration solution for a two-source situation where source variability also is included. A general observation from this examination is that the variability of the source profiles not only affects the calculated precision but also the mean/median source contributions.
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| 8. |
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| 9. |
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| 10. |
- Andersson, August, et al.
(författare)
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Magnetic resonance investigations of lipid motion in isotropic bicelles
- 2005
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 21:7, s. 7702-7709
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of DMPC in different isotropic bicelles have been investigated by NMR and EPR methods. The local dynamics were obtained by interpretation of 13C NMR relaxation measurements of DMPC in the bicelles, and these results were compared to EPR spectra of spin-labeled lipids. The overall size of the bicelles was investigated by PFG NMR translational diffusion measurements. The dynamics and relative sizes were compared among three different bicelles: [DMPC]/[DHPC] = 0.25, [DMPC]/[DHPC] = 0.5, and [DMPC]/[CHAPS] = 0.5. The local motion is found to depend much more strongly on the choice of the detergent, rather than the overall size of the bicelle. The results provide an explanation for differences in apparent dynamics for different peptides, which are bound to bicelles. This in turn determines under what conditions reasonable NMR spectra can be observed. A model is presented in which extensive local motion, in conjunction with the overall size, affects the spectral properties. An analytical expression for the size dependence of the bicelles, relating the radius of the bilayer region with physical properties of the detergent and the lipid, is also presented.
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| 11. |
- Andersson, August
(författare)
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Mechanisms for log normal concentration distributions in the environment
- 2021
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Log normal-like concentration distributions are ubiquitously observed in the environment. However, the mechanistic origins are not well understood. In this paper, we show that first order exponential kinetics onsets log-normal concentration distributions, under certain assumptions. Given the ubiquity of exponential kinetics, e.g., source and sink processes, this model suggests an explanation for the frequent observation in the environment, and elsewhere. We compare this model to other mechanisms affecting concentration distributions, e.g., source mixing. Finally, we discuss possible implications for data analysis and modelling, e.g., log-normal rates and fluxes.
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| 12. |
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| 13. |
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| 14. |
- Andersson, August, et al.
(författare)
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Regionally-Varying Combustion Sources of the January 2013 Severe Haze Events over Eastern China
- 2015
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 49:4, s. 2038-2043
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Tidskriftsartikel (refereegranskat)abstract
- Thick haze plagued northeastern China in January 2013, strongly affecting both regional climate and human respiratory health. Here, we present dual carbon isotope constrained (Delta C-14 and delta C-13) source apportionment for combustion-derived black carbon aerosol (BC) for three key hotspot regions (megacities): North China Plain (NCP, Beijing), the Yangtze River Delta (YRD, Shanghai), and the Pearl River Delta (PRD, Guangzhou) for January 2013. BC, here quantified as elemental carbon (EC), is one of the most health-detrimental components of PM2.5 and a strong climate warming agent. The results show that these severe haze events were equally affected (similar to 30%) by biomass combustion in all three regions, whereas the sources of the dominant fossil fuel component was dramatically different between north and south. In the NCP region, coal combustion accounted for 66% (46-74%, 95% C.I.) of the EC, whereas, in the YRD and PRD regions, liquid fossil fuel combustion (e.g., traffic) stood for 46% (18-66%) and 58% (38-68%), respectively. Taken together, these findings suggest the need for a regionally-specific description of BC sources in climate models and regionally-tailored mitigation to combat severe air pollution events in East Asia.
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| 15. |
- Andersson, August, et al.
(författare)
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Seasonal source variability of carbonaceous aerosols at the Rwanda Climate Observatory
- 2020
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 20:8, s. 4561-4573
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Tidskriftsartikel (refereegranskat)abstract
- Sub-Saharan Africa (SSA) is a global hot spot for aerosol emissions, which affect the regional climate and air quality. In this paper, we use ground-based observations to address the large uncertainties in the source-resolved emission estimation of carbonaceous aerosols. Ambient fine fraction aerosol was collected on filters at the high-altitude (2590 m a.s.1.) Rwanda Climate Observatory (RCO), a SSA background site, during the dry and wet seasons in 2014 and 2015. The concentrations of both the carbonaceous and inorganic ion components show a strong seasonal cycle, with highly elevated concentrations during the dry season. Source marker ratios, including carbon isotopes, show that the wet and dry seasons have distinct aerosol compositions. The dry season is characterized by elevated amounts of biomass burning products, which approach similar to 95 % for carbonaceous aerosols. An isotopic mass-balance estimate shows that the amount of the carbonaceous aerosol stemming from savanna fires may increase from 0.2 mu g m(-3) in the wet season up to 10 mu g m(-3) during the dry season. Based on these results, we quantitatively show that savanna fire is the key modulator of the seasonal aerosol composition variability at the RCO.
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| 16. |
- Andersson, August, 1974-
(författare)
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The Application of isotropic bicelles as model membranes
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Isotropic bicelles are disc-shaped aggregates of lipids and detergents, and are suitable model systems for high-resolution NMR studies of membrane-interacting peptides. In this thesis the structures for the two peptides motilin and transportan were determined by homonuclear 1H methods in the presence of bicelles, and the structure of the bovine prion protein peptide (bPrPp) was solved in the presence of DHPC micelles. All of these peptides were found to be largely a-helical when bound to the model membranes. In subsequent experiments both motilin and transportan were shown to reside on the surface of the bicelles, whereas bPrPp is more likely to have a transmembrane configuration. NMR translational diffusion experiments revealed that the isotropic bicelles studied here are very large objects compared to what is regularly indicated by high-resolution NMR spectroscopy. Furthermore, these studies showed that all three peptides examined interact strongly with bicelles. Investigation of the NMR-relaxation of labeled sites in the peptides motilin and penetratin demonstrated that the overall rotational correlation times for these peptides do not reflect the bicellar size. Such decoupling of NMR relaxation from the dependence of overall size is also seen for the dynamics of the lipid molecules in the bicelles. It is therefore concluded that the overall size is not the sole determinant of the linewidths in NMR spectra, but that extensive motions within the bicelles also exert significant effects. Another interesting observation is that the membrane-bound structures of the peptides motilin, transportan, penetratin and bPrPp are very similar, even though these peptides have very different biological functions. In contrast, considerably more variation is observed in the membrane-positioning and molecular dynamics of these peptides. Since the bicelles have been found to induce differences in membrane positioning and molecular dynamics compared to micelles, these model membranes are likely to be important in order to enhance our understanding of the biological function of membrane interacting peptides.
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| 17. |
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| 18. |
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| 19. |
- Andersson, Tim, et al.
(författare)
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Road Boundary Detection Using Ant Colony Optimization Algorithm
- 2020
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Ingår i: Advances in Natural Computation, Fuzzy Systems and Knowledge Discovery. - Cham : Springer. - 9783030324551 ; , s. 409-416
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Konferensbidrag (refereegranskat)abstract
- A common problem for autonomous vehicles is to define a coherent round boundary of unstructured roads. To solve this problem an evolutionary approach has been evaluated, by using a modified ant optimization algorithm to define a coherent road edge along the unstructured road in night conditions. The work presented in this paper involved pre-processing, perfecting the edges in an autonomous fashion and developing an algorithm to find the best candidates of starting positions for the ant colonies. All together these efforts enable ant colony optimization (ACO) to perform successfully in this application scenario. The experiment results show that the best paths well followed the edges and that the mid-points between the paths stayed centered on the road.
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| 20. |
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| 21. |
- Bárány-Wallje, Elsa, et al.
(författare)
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Dynamics of transportan in bicelles is surface charge dependent.
- 2006
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Ingår i: J Biomol NMR. - 0925-2738. ; 35:2, s. 137-47
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Tidskriftsartikel (refereegranskat)abstract
- In this study we investigated the dynamic behavior of the chimeric cell-penetrating peptide transportan in membrane-like environments using NMR. Backbone amide 15N spin relaxation was used to investigate the dynamics in two bicelles: neutral DMPC bicelles and partly negatively charged DMPG-containing bicelles.The structure of the peptide as judged from CD and chemical shifts is similar in the two cases. Both the overall motion as well as the local dynamics is, however, different in the two types of bicelles. The overall dynamics of the peptide is significantly slower in the partly negatively charged bicelle environment, as evidenced by longer global correlation times for all measured sites.The local motion, as judged from generalized order parameters, is for all sites in the peptide more restricted when bound to negatively charged bicelles than when bound to neutral bicelles (increase in S2 is on average 0.11±0.07). The slower dynamics of transportan in charged membrane model systems cause significant line broadening in the proton NMR spectrum, which in certain cases limits the observation of 1H signals for transportan when bound to the membrane. The effect of transportan on DMPC and DHPC motion in zwitterionic bicelles was also investigated, and the motion of both components in the bicelle was found to be affected.
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| 22. |
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| 23. |
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| 24. |
- Bárány-Wallje, Elsa, et al.
(författare)
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NMR solution structure and position of transportan in neutral phospholipid bicelles.
- 2004
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Ingår i: FEBS Lett. - 0014-5793. ; 567:2-3, s. 265-9
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Tidskriftsartikel (refereegranskat)abstract
- Transportan is a chimeric cell-penetrating peptide constructed from the peptides galanin and mastoparan, which has the ability to internalize living cells carrying a hydrophilic load. In this study, we have determined the NMR solution structure and investigated the position of transportan in neutral bicelles. The structure revealed a well-defined -helix in the C-terminal mastoparan part of the peptide and a weaker tendency to form an -helix in the N-terminal domain. The position of the peptide in relation to the membrane, as studied by adding paramagnetic probes, shows that the peptide lies parallel to, and in the head-group region of the membrane surface. This result is supported by amide proton secondary chemical shifts.
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| 25. |
- Bikkina, Srinivas, et al.
(författare)
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Air quality in megacity Delhi affected by countryside biomass burning
- 2019
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Ingår i: Nature Sustainability. - : Springer Science and Business Media LLC. - 2398-9629. ; 2:3, s. 200-205
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Tidskriftsartikel (refereegranskat)abstract
- South Asian megacities are strong sources of regional air pollution. Delhi is a key hotspot of health-and climate-impacting black carbon (BC) emissions, affecting environmental sustainability in densely populated northern India. Effective mitigation of BC impact is hampered by highly uncertain emission source estimates. Here, we use dual-carbon isotope fingerprints (delta C-13/Delta C-14) of BC to constrain the seasonal source variability in Delhi. These measurements show that lower BC concentrations in summer are predominantly from fossil fuel sources (similar to 83%). However, large-scale open burning of post-harvest crop residue/wood in nearby rural regions is contributing to severe haze pollution in Delhi during winter and autumn (similar to 42 +/- 17%). Hence, the common conception that megacities affect their surroundings is here amended or seasonally reversed. Therefore, to combat the severe air pollution problems in Delhi and the environmental quality of northern India, current urban efforts need to be complemented with countryside regional mitigation.
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