| 21. |
- Ahlberg, Erik, et al.
(författare)
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Secondary organic aerosol from VOC mixtures in an oxidation flow reactor
- 2017
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Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310. ; 161, s. 210-220
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Tidskriftsartikel (refereegranskat)abstract
- The atmospheric organic aerosol is a tremendously complex system in terms of chemical content. Models generally treat the mixtures as ideal, something which has been questioned owing to model-measurement discrepancies. We used an oxidation flow reactor to produce secondary organic aerosol (SOA) mixtures containing oxidation products of biogenic (α-pinene, myrcene and isoprene) and anthropogenic (m-xylene) volatile organic compounds (VOCs). The resulting volume concentration and chemical composition was measured using a scanning mobility particle sizer (SMPS) and a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), respectively. The SOA mass yield of the mixtures was compared to a partitioning model constructed from single VOC experiments. The single VOC SOA mass yields with no wall-loss correction applied are comparable to previous experiments. In the mixtures containing myrcene a higher yield than expected was produced. We attribute this to an increased condensation sink, arising from myrcene producing a significantly higher number of nucleation particles compared to the other precursors. Isoprene did not produce much mass in single VOC experiments but contributed to the mass of the mixtures. The effect of high concentrations of isoprene on the OH exposure was found to be small, even at OH reactivities that previously have been reported to significantly suppress OH exposures in oxidation flow reactors. Furthermore, isoprene shifted the particle size distribution of mixtures towards larger sizes, which could be due to a change in oxidant dynamics inside the reactor.
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| 22. |
- Ahlberg, Erik
(författare)
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Speeding up the Atmosphere : Experimental oxidation studies of ambient and laboratory aerosols using a flow reactor
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Apart from gases, the air we breath consist of tiny, so called, aerosol particles. A cubic metre of air in a relatively clean environment can consist of several billion aerosol particles. The impact of these particles on human health and on climate is significant. According to WHO, particles affect more humans than any other pollutant, and is closely related to mortality and morbidity. Further, it has been estimated that anthropogenic particles have cooled the climate, masking up to 50% of the warming caused by greenhouse gases. A large portion of the smallest particles consists of organic compounds, much of which is formed by atmospheric oxidation reactions. This material is called secondary organic aerosol (SOA). In this thesis, submicron secondary aerosol particles have been investigated using an oxidation flow reactor (OFR). Inside the reactor, large concentrations of oxidants produce secondary particulate material in a matter of minutes, thereby speeding up the naturally occuring atmospheric processes.In two laboratory studies, we have investigated the effect of mixing anthropogenic primary and secondary particles with biogenic SOA. In line with expectations, the anthropogenic and biogenic organic precursors mixed, and, in a non-linear way, formed more particulate mass than would otherwise be the case. Further, the effect of wet anthropogenic salt particles on SOA formation was investigated. The produced SOA mass in the presence of wet particles was significantly higher than if the particles were dry. This effect is believed to be very important in the atmosphere since water is always present. In both these studies it was shown that the SOA mass formed in OFRs at low particle mass concentrations, is underestimated due to the limited time for condensation of vapours in the reactor.In a separate study, the SOA formation from biomass burning was investigated. Biogenic SOA dominates on a global scale, but very high concentrations are only formed in the proximity of anthropogenic sources. It was shown that SOA formation from the emissions of a modern wood stove can be large enough to dominate over the primary particle emissions. To estimate the secondary particle formation potential of ambient air, two field studies were performed. In both studies, the simulated atmospheric processing of the background air did not produce much secondary particle mass. From this, it can be concluded that the chosen measurement sites were relatively clean, but the results also point to the efficiency of atmospheric processing. However, in one of the studies, targeting ship emissions at a coastal site, plumes of secondary material, of the same magnitude as the background aerosol particle concentration, was formed. This demonstrates the importance of considering atmospheric processing and the advantage of using OFRs in field studies.The relative importance of SOA in the atmospheric aerosol is believed to increase in the future. Due to complex feedbacks and the many variables affecting SOA formation, it is difficult to parameterize in a simple enough manner fit for global models. Both detailed and large-scale processes needs further investigation to improve estimations of SOA radiative forcing and the anthropogenic effect on biogenic SOA. The popularity of oxidation flow reactors in SOA research is likely to increase. The five original research manuscripts included in this thesis contributes specifically to the OFR research community, but also to improved understanding of SOA formation in the the anthropocene in general.
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| 23. |
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| 24. |
- Ahlberg, Martina, et al.
(författare)
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Reversed interface effects in amorphous FeZr/AlZr multilayers
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 90:18, s. 184403-
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Tidskriftsartikel (refereegranskat)abstract
- We report an anomalous enhancement of the critical temperature (T-c) when the thickness (d) of the magnetic layer is decreased from 60 to 20 angstrom in amorphous FeZr/AlZr multilayers. Further reduction of the thickness causes a decrease of T-c, as expected by finite-size scaling, while the magnetic moment decreases monotonically for all values of d. The increase of the critical temperature is attributed to a reversed interface effect where local changes in the nearest-neighbor distance and coordination number gives a higher effective magnetic coupling at the interfaces compared to the interior of the layer. We have successfully described the results within a model where such interface effects are combined with finite-size scaling.
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| 25. |
- Ahlberg, Mats Steinholtz, et al.
(författare)
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Time without PSA recurrence after radical prostatectomy as a predictor of future biochemical recurrence, metastatic disease and prostate cancer death : a prospective Scandinavian cohort study
- 2022
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Ingår i: BMJ Open. - : BMJ Publishing Group Ltd. - 2044-6055. ; 12:12
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Tidskriftsartikel (refereegranskat)abstract
- Objective: Although surveillance after radical prostatectomy routinely includes repeated prostate specific antigen (PSA)-testing for many years, biochemical recurrence often occurs without further clinical progression. We therefore hypothesised that follow-up can be shortened for many patients without increasing the risk of prostate cancer death. We investigated the long-term probabilities of PSA recurrence, metastases and prostate cancer death in patients without biochemical recurrence five and 10 years after radical prostatectomy.Design: Prospective cohort study. Stratification by Gleason score (<= 3+4=7or >= 4+3=7), pathological tumour stage (pT2 or >= pT3) and negative or positive surgical margins.Setting: Between 1989 and 1998, 14 urological centres in Scandinavia randomised patients to the Scandinavian Prostate Cancer Group study number 4 (SPCG-4) trial.ParticipationAll 306 patients from the SPCG-4 trial who underwent radical prostatectomy within 1year from inclusion were eligible. Four patients were excluded due to surgery-related death (n=1) or salvage radiotherapy or hormonal treatment within 6weeks from surgery (n=3).Primary outcome measures: Cumulative incidences and absolute differences in metastatic disease and prostate cancer death.Results: We analysed 302 patients with complete follow-up during a median of 24 years. Median preoperative PSA was 9.8ng/mL and median age was 65 years. For patients without biochemical recurrence 5 years after radical prostatectomy the 20-year probability of biochemical recurrence was 25% among men with Gleason score <= 3+4=7and 57% among men with Gleason score >= 4+3=7; the probabilities for metastases were 0.8% and 17%; and for prostate cancer death 0.8% and 12%, respectively. The long-term probabilities were higher for pT >= 3versus pT2 and for positive versus negative surgical margins. Limitations include small size of the cohort.Conclusion: Many patients with favourable histopathology without biochemical recurrence 5years after radical prostatectomy could stop follow-up earlier than 10 years after radical prostatectomy.
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| 26. |
- Ahlberg, Per Erik
(författare)
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Glimpsing the hidden majority
- 1990
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Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 344, s. 23-
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 27. |
- Ahlberg, Per Erik, 1963-
(författare)
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Humeral homology and the origin of the tetrapod elbow : a reinterpretation of the enigmatic specimens ANSP 21350 and GSM 104536
- 2011
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Ingår i: Studies on fossil tetrapods. - London : The Palaeontological Association. - 9781444361896 ; , s. 17-29
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Bokkapitel (refereegranskat)abstract
- Two putative tetrapod humeri of Devonian age, ANSP 21350 from the late Famennian of Pennsylvania and GSM 104536 from the late Frasnian of Scat Craig, Scotland, are reinterpreted in the light of more recent discoveries. The morphology of ANSP 21350 can be more fully homologized with those of elpistostegids and early tetrapods than previously recognized. Unique features include distally displaced dorsal muscle attachments and a ventrally rotated distal face of the bone. This suggests that a weight-bearing ventrally directed forearm was created, not by means of a flexed elbow as in other tetrapods, but by distorting the humerus. The olecranon process on the ulna was probably poorly developed or absent. Primitive characters that are absent in other tetrapods add support to the contention that ANSP 21350 is the least crownward of known tetrapod humeri. Contrary to previous claims, Acanthostega has a characteristic tetrapod ulnar morphology with an olecranon process; it does not resemble an elpistostegid ulna and is not uniquely primitive for tetrapods. This suggests that the flexed tetrapod elbow with ulnar extensor muscles attached to the olecranon evolved simultaneously with the large rectangular entepicondyle typical for early tetrapods, probably as part of a single functional complex. GSM 104536 is denfinitely not a primitive tetrapod humerus, nor a sarcopterygian branchial bone, but cannot be positively identified at present.
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| 28. |
- Ahlberg, Per Erik, 1963-, et al.
(författare)
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Pelvic claspers confirm chondrichthyan-like internal fertilization in arthrodires
- 2009
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Ingår i: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 460:7257, s. 888-889
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Tidskriftsartikel (refereegranskat)abstract
- Recent finds(1,2) demonstrate that internal fertilization and viviparity (live birth) were more widespread in the Placodermi, an extinct group of armoured fishes, than was previously realized. Placoderms represent the sister group of the crown group jawed vertebrates (Gnathostomata)(3,4), making their mode(s) of reproduction potentially informative about primitive gnathostome conditions. An ossified pelvic fin basipterygium discovered in the arthrodire Incisoscutum ritchiei was hypothesized to be identical in males and females, with males presumed to have an additional cartilaginous element or series forming a clasper. Here we report the discovery of a completely ossified pelvic clasper in Incisoscutum ritchiei (WAM 03.3.28) which shows that this interpretation was incorrect: the basipterygium described previously(1) is in fact unique to females. The male clasper is a slender rod attached to a square basal plate that articulates directly with the pelvis. It carries a small cap of dermal bone covered in denticles and small hooks that may be homologous with the much larger dermal component of the ptyctodont clasper.
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| 29. |
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| 30. |
- Ahlgren, Björn, et al.
(författare)
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Testing a model for subphotospheric dissipation in GRBs: fits to Fermi data constrain the dissipation scenario
- 2019
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 485, s. 474-497
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Tidskriftsartikel (refereegranskat)abstract
- It has been suggested that the prompt emission in gamma-ray bursts (GRBs) could be described by radiation from the photosphere in a hot fireball. Such models must be tested by directly fitting them to data. In this work we use data from the Fermi Gamma-ray Space Telescope and consider a specific photospheric model, in which the kinetic energy of a low-magnetization outflow is dissipated locally by internal shocks below the photosphere. We construct a table model with a physically motivated parameter space and fit it to time-resolved spectra of the 36 brightest Fermi GRBs with a known redshift. We find that about two-thirds of the examined spectra cannot be described by the model, as it typically underpredicts the observed flux. However, since the sample is strongly biased towards bright GRBs, we argue that this fraction will be significantly lowered when considering the full population. From the successful fits we find that the model can reproduce the full range of spectral slopes present in the sample. For these cases we also find that the dissipation consistently occurs at a radius of ∼1012 cm and that only a few per cent efficiency is required. Furthermore, we find a positive correlation between the fireball luminosity and the Lorentz factor. Such a correlation has been previously reported by independent methods. We conclude that if GRB spectra are due to photospheric emission, the dissipation cannot only be the specific scenario we consider here.
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