| 1. |
- Ahlberg, Erik, et al.
(author)
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"Vi klimatforskare stödjer Greta och skolungdomarna"
- 2019
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In: Dagens nyheter (DN debatt). - 1101-2447.
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Journal article (pop. science, debate, etc.)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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| 3. |
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| 4. |
- Martinsson, Johan, et al.
(author)
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Impacts of Combustion Conditions and Photochemical Processing on the Light Absorption of Biomass Combustion Aerosol
- 2015
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In: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 49:24, s. 14663-14671
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Journal article (peer-reviewed)abstract
- The aim was to identify relationships between combustion conditions, particle characteristics, and optical properties of fresh and photochemically processed emissions from biomass combustion. The combustion conditions included nominal and high burn rate operation and individual combustion phases from a conventional wood stove. Low temperature pyrolysis upon fuel addition resulted in "tar-ball" type particles dominated by organic aerosol with an absorption Angstrom exponent (AAE) of 2.5-2.7 and estimated Brown Carbon contributions of 50-70% to absorption at the climate relevant aethalometer-wavelength (520 nm). High temperature combustion during the intermediate (flaming) phase was dominated by soot agglomerates with AAE 1.0-1.2 and 85-100% of absorption at 520 nm attributed to Black Carbon. Intense photochemical processing of high burn rate flaming combustion emissions in an oxidation flow reactor led to strong formation of Secondary Organic Aerosol, with no or weak absorption. PM1 mass emission factors (mg/kg) of fresh emissions were about an order of magnitude higher for low temperature pyrolysis compared to high temperature combustion. However, emission factors describing the absorption cross section emitted per kg of fuel consumed (m(2)/kg) were of similar magnitude at 520 nm for the diverse combustion conditions investigated in this study. These results provide a link between biomass combustion conditions, emitted particle types, and their optical properties in fresh and processed plumes which can be of value for source apportionment and balanced mitigation of biomass combustion emissions from a climate and health perspective.
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| 7. |
- Nilsson, Lovisa, et al.
(author)
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Relating the single particle soot photometer (SP2) signal response to soot maturity
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In: Aerosol Science and Technology. - 1521-7388.
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Journal article (peer-reviewed)abstract
- Light absorbing carbonaceous aerosols produced from combustion span over a range of physicochemical properties. Soot is the most recognized species in this category and its formation process involves gradual maturation from amorphous young soot with a high hydrogen-to-carbon-ratio toward mature soot aggregates. In this work, the optical response of a single particle soot photometer (SP2) to electrical mobility size selected soot of different maturity produced by a mini-CAST soot generator is investigated. The results show that for soot of a specific mobility diameter, the laser-induced incandescence (LII) signal appears earlier and with a higher LII peak height for increasing soot maturity. The experimental observations are supported by simulations using a numerical model for the LII process. Furthermore, the effect of systematically varying the SP2 laser power on the detection of soot of different maturity using LII is explored. This work can be seen as a step toward the aim of using the SP2 instrument to identify soot particles of different maturity in the atmosphere.
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| 8. |
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| 9. |
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| 10. |
- Ahlberg, Erik, et al.
(author)
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Measurement report : Black carbon properties and concentrations in southern Sweden urban and rural air-the importance of long-range transport
- 2023
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In: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 23:5, s. 3051-3064
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Journal article (peer-reviewed)abstract
- Soot, or black carbon (BC), aerosol is a major climate forcer with severe health effects. The impacts depend strongly on particle number concentration, size and mixing state. This work reports on two field campaigns at nearby urban and rural sites, 65gkm apart, in southern Sweden during late summer 2018. BC was measured using a single-particle soot photometer (SP2) and Aethalometers (AE33). Differences in BC concentrations between the sites are driven primarily by local traffic emissions. Equivalent and refractory BC mass concentrations at the urban site were on average a factor 2.2 and 2.5, with peaks during rush hour up to a factor g1/44, higher than the rural background levels. The number fraction of particles containing a soot core was significantly higher in the city. BC particles at the urban site were on average smaller by mass and had less coating owing to fresh traffic emissions. The organic components of the fresh traffic plumes were similar in mass spectral signature to hydrocarbon-like organic aerosol (HOA), commonly associated with traffic. Despite the intense local traffic (g1/4g30g000 vehicles passing per day), PM1, including organic aerosol, was dominated by aged continental air masses even at the curbside site. The fraction of thickly coated particles at the urban site was highly correlated with the mass concentrations of all measured chemical species of PM1, consistent with aged, internally mixed aerosol. Trajectory analysis for the whole year showed that air masses arriving at the rural site from eastern Europe contained approximately double the amount of BC compared to air masses from western Europe. Furthermore, the largest regional emissions of BC transported to the rural site, from the Malmö-Copenhagen urban area, are discernible above background levels only when precipitation events are excluded. We show that continental Europe and not the Malmö-Copenhagen region is the major contributor to the background BC mass concentrations in southern Sweden.
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| 13. |
- Martinsson, Johan, et al.
(author)
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Carbonaceous aerosol source apportionment using the Aethalometer model - evaluation by radiocarbon and levoglucosan analysis at a rural background site in southern Sweden
- 2017
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In: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 17:6, s. 4265-4281
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Journal article (peer-reviewed)abstract
- With the present demand on fast and inexpensive aerosol source apportionment methods, the Aethalometer model was evaluated for a full seasonal cycle (June 2014June 2015) at a rural atmospheric measurement station in southern Sweden by using radiocarbon and levoglucosan measurements. By utilizing differences in absorption of UV and IR, the Aethalometer model apportions carbon mass into wood burning (WB) and fossil fuel combustion (FF) aerosol. In this study, a small modification in the model in conjunction with carbon measurements from thermal-optical analysis allowed apportioned non-light-absorbing biogenic aerosol to vary in time. The absorption differences between WB and FF can be quantified by the absorption angstrom ngstrom exponent (AAE). In this study AAE(WB) was set to 1.81 and AAE(FF) to 1.0. Our observations show that the AAE was elevated during winter (1.36 +/- 0.07) compared to summer (1.12 +/- 0.07). Quantified WB aerosol showed good agreement with levoglucosan concentrations, both in terms of correlation (R-2 = 0 : 70) and in comparison to reference emission inventories. WB aerosol showed strong seasonal variation with high concentrations during winter (0.65 mu gm(-3), 56% of total carbon) and low concentrations during summer (0.07 mu gm(-3), 6% of total carbon). FF aerosol showed less seasonal dependence; however, black carbon (BC) FF showed clear diurnal patterns corresponding to traffic rush hour peaks. The presumed non-light-absorbing biogenic carbonaceous aerosol concentration was high during summer (1.04 mu gm(-3), 72% of total carbon) and low during winter (0.13 mu gm(-3), 8% of total carbon). Aethalometer model results were further compared to radiocarbon and levoglucosan source apportionment results. The comparison showed good agreement for apportioned mass of WB and biogenic carbonaceous aerosol, but discrepancies were found for FF aerosol mass. The Aethalometer model overestimated FF aerosol mass by a factor of 1.3 compared to radiocarbon and levoglucosan source apportionment. A performed sensitivity analysis suggests that this discrepancy can be explained by interference of non-light-absorbing biogenic carbon during winter. In summary, the Aethalometer model offers a costeffective yet robust high-time-resolution source apportionment at rural background stations compared to a radiocarbon and levoglucosan alternative.
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| 14. |
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| 15. |
- Ringaby, Erik, et al.
(author)
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Co-aligning Aerial Hyperspectral Push-broom Strips for Change Detection
- 2010
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In: Proc. SPIE 7835, Electro-Optical Remote Sensing, Photonic Technologies, and Applications IV. - : SPIE - International Society for Optical Engineering. - 9780819483539 ; , s. Art.nr. 7835B-36-
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Conference paper (peer-reviewed)abstract
- We have performed a field trial with an airborne push-broom hyperspectral sensor, making several flights over the same area and with known changes (e.g., moved vehicles) between the flights. Each flight results in a sequence of scan lines forming an image strip, and in order to detect changes between two flights, the two resulting image strips must be geometrically aligned and radiometrically corrected. The focus of this paper is the geometrical alignment, and we propose an image- and gyro-based method for geometric co-alignment (registration) of two image strips. The method is particularly useful when the sensor is not stabilized, thus reducing the need for expensive mechanical stabilization. The method works in several steps, including gyro-based rectification, global alignment using SIFT matching, and a local alignment using KLT tracking. Experimental results are shown but not quantified, as ground truth is, by the nature of the trial, lacking.
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| 16. |
- Ringaby, Erik, et al.
(author)
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Co-alignmnent of Aerial Push-broom Strips using Trajectory Smoothness Constraints
- 2010
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Conference paper (other academic/artistic)abstract
- We study the problem of registering a sequence of scan lines (a strip) from an airborne push-broom imager to another sequence partly covering the same area. Such a registration has to compensate for deformations caused by attitude and speed changes in the aircraft. The registration is challenging, as both strips contain such deformations. Our algorithm estimates the 3D rotation of the camera for each scan line, by parametrising it as a linear spline with a number of knots evenly distributed in one of the strips. The rotations are estimated from correspondences between strips of the same area. Once the rotations are known, they can be compensated for, and each line of pixels can be transformed such that ground trace of the two strips are registered with respect to each other.
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| 17. |
- Abera, Asmamaw, et al.
(author)
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Air pollution measurements and land-use regression in urban sub-saharan Africa using low-cost sensors—possibilities and pitfalls
- 2020
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In: Atmosphere. - : MDPI AG. - 2073-4433. ; 11:12
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Journal article (peer-reviewed)abstract
- Air pollution is recognized as the most important environmental factor that adversely affects human and societal wellbeing. Due to rapid urbanization, air pollution levels are increasing in the Sub-Saharan region, but there is a shortage of air pollution monitoring. Hence, exposure data to use as a base for exposure modelling and health effect assessments is also lacking. In this study, low-cost sensors were used to assess PM2.5 (particulate matter) levels in the city of Adama, Ethiopia. The measurements were conducted during two separate 1-week periods. The measurements were used to develop a land-use regression (LUR) model. The developed LUR model explained 33.4% of the variance in the concentrations of PM2.5. Two predictor variables were included in the final model, of which both were related to emissions from traffic sources. Some concern regarding influential observations remained in the final model. Long-term PM2.5 and wind direction data were obtained from the city’s meteorological station, which should be used to validate the representativeness of our sensor measurements. The PM2.5 long-term data were however not reliable. Means of obtaining good reference data combined with longer sensor measurements would be a good way forward to develop a stronger LUR model which, together with improved knowledge, can be applied towards improving the quality of health. A health impact assessment, based on the mean level of PM2.5 (23 µg/m3), presented the attributable burden of disease and showed the importance of addressing causes of these high ambient levels in the area.
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| 18. |
- Ahlberg, Daniel, 1982, et al.
(author)
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Noise sensitivity in continuum percolation
- 2014
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In: Israel Journal of Mathematics. - : Springer Science and Business Media LLC. - 0021-2172 .- 1565-8511. ; 201:2, s. 847-899
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Journal article (peer-reviewed)abstract
- We prove that the Poisson Boolean model, also known as the Gilbert disc model, is noise sensitive at criticality. This is the first such result for a Continuum Percolation model, and the first which involves a percolation model with critical probability pc not equal 1/2. Our proof uses a version of the Benjamini-Kalai-Schramm Theorem for biased product measures. A quantitative version of this result was recently proved by Keller and Kindler. We give a simple deduction of the non-quantitative result from the unbiased version. We also develop a quite general method of approximating Continuum Percolation models by discrete models with pc bounded away from zero; this method is based on an extremal result on non-uniform hypergraphs.
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| 19. |
- Ahlberg, Erik, et al.
(author)
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Effect of salt seed particle surface area, composition and phase on secondary organic aerosol mass yields in oxidation flow reactors
- 2019
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In: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 19:4, s. 2701-2712
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Journal article (peer-reviewed)abstract
- Atmospheric particulate water is ubiquitous, affecting particle transport and uptake of gases. Yet, research on the effect of water on secondary organic aerosol (SOA) mass yields is not consistent. In this study, the SOA mass yields of an α-pinene and m-xylene mixture, at a concentration of 60 μgm-3, were examined using an oxidation flow reactor operated at a relative humidity (RH) of 60% and a residence time of 160 s. Wet or dried ammonium sulfate and ammonium nitrate seed particles were used. By varying the amount of seed particle surface area, the underestimation of SOA formation induced by the short residence time in flow reactors was confirmed. Starting at a SOA mass concentration of 5 μgm-3, the maximum yield increased by a factor of 2 with dry seed particles and on average a factor of 3.2 with wet seed particles. Hence, wet particles increased the SOA mass yield by 60% compared to the dry experiment. Maximum yield in the reactor was achieved using a surface area concentration of 1600 μm2 cm-3. This corresponded to a condensational lifetime of 20 s for low-volatility organics. The O V C ratio of SOA on wet ammonium sulfate was significantly higher than when using ammonium nitrate or dry ammonium sulfate seed particles, probably due to differences in heterogeneous chemistry.
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| 20. |
- Ahlberg, Erik, et al.
(author)
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No particle mass enhancement from induced atmospheric ageing at a rural site in northern Europe
- 2019
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In: Atmosphere. - : MDPI AG. - 2073-4433. ; 10:7
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Journal article (peer-reviewed)abstract
- A large portion of atmospheric aerosol particles consists of secondary material produced by oxidation reactions. The relative importance of secondary organic aerosol (SOA) can increase with improved emission regulations. A relatively simple way to study potential particle formation in the atmosphere is by using oxidation flow reactors (OFRs) which simulate atmospheric ageing. Here we report on the first ambient OFR ageing experiment in Europe, coupled with scanning mobility particle sizer (SMPS), aerosol mass spectrometer (AMS) and proton transfer reaction (PTR)-MS measurements. We found that the simulated ageing did not produce any measurable increases in particle mass or number concentrations during the two months of the campaign due to low concentrations of precursors. Losses in the reactor increased with hydroxyl radical (OH) exposure and with increasing difference between ambient and reactor temperatures, indicating fragmentation and evaporation of semivolatile material.
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| 21. |
- Ahlberg, Erik, et al.
(author)
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Secondary organic aerosol from VOC mixtures in an oxidation flow reactor
- 2017
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In: Atmospheric Environment. - : Elsevier BV. - 1352-2310. ; 161, s. 210-220
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Journal article (peer-reviewed)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
(author)
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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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Doctoral thesis (other academic/artistic)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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| 24. |
- Ahlberg, Martina, et al.
(author)
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Reversed interface effects in amorphous FeZr/AlZr multilayers
- 2014
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 90:18, s. 184403-
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Journal article (peer-reviewed)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.
(author)
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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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In: BMJ Open. - : BMJ Publishing Group Ltd. - 2044-6055. ; 12:12
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Journal article (peer-reviewed)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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