| 1. |
- Niemi, MEK, et al.
(författare)
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- 2021
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swepub:Mat__t
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| 2. |
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| 3. |
- Luterbacher, J., et al.
(författare)
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European summer temperatures since Roman times
- 2016
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Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 11:2
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Tidskriftsartikel (refereegranskat)abstract
- The spatial context is criticalwhen assessing present-day climate anomalies, attributing them to potential forcings and making statements regarding their frequency and severity in a long-term perspective. Recent international initiatives have expanded the number of high-quality proxy-records and developed new statistical reconstruction methods. These advances allow more rigorous regional past temperature reconstructions and, in turn, the possibility of evaluating climate models on policy-relevant, spatiotemporal scales. Here we provide a new proxy-based, annually-resolved, spatial reconstruction of the European summer (June-August) temperature fields back to 755 CE based on Bayesian hierarchical modelling (BHM), together with estimates of the European mean temperature variation since 138 BCE based on BHM and composite-plus-scaling (CPS). Our reconstructions compare well with independent instrumental and proxy-based temperature estimates, but suggest a larger amplitude in summer temperature variability than previously reported. Both CPS and BHM reconstructions indicate that the mean 20th century European summer temperature was not significantly different from some earlier centuries, including the 1st, 2nd, 8th and 10th centuries CE. The 1st century (in BHM also the 10th century) may even have been slightly warmer than the 20th century, but the difference is not statistically significant. Comparing each 50 yr period with the 1951-2000 period reveals a similar pattern. Recent summers, however, have been unusually warm in the context of the last two millennia and there are no 30 yr periods in either reconstruction that exceed the mean average European summer temperature of the last 3 decades (1986-2015 CE). A comparison with an ensemble of climate model simulations suggests that the reconstructed European summer temperature variability over the period 850-2000 CE reflects changes in both internal variability and external forcing on multi-decadal time-scales. For pan-European temperatures we find slightly better agreement between the reconstruction and the model simulations with high-end estimates for total solar irradiance. Temperature differences between the medieval period, the recent period and the Little Ice Age are larger in the reconstructions than the simulations. This may indicate inflated variability of the reconstructions, a lack of sensitivity and processes to changes in external forcing on the simulated European climate and/or an underestimation of internal variability on centennial and longer time scales.
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| 6. |
- Valiente-Dobon, J. J., et al.
(författare)
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Lifetime Measurements of the Neutron-Rich N=30 Isotones Ca-50 and Sc-51: Orbital Dependence of Effective Charges in the fp Shell
- 2009
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Ingår i: Physical Review Letters. - 1079-7114. ; 102:24
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Tidskriftsartikel (refereegranskat)abstract
- The lifetimes of the first excited states of the N=30 isotones Ca-50 and Sc-51 have been determined using the Recoil Distance Doppler Shift method in combination with the CLARA-PRISMA spectrometers. This is the first time such a method is applied to measure lifetimes of neutron-rich nuclei populated via a multinucleon transfer reaction. This extends the lifetime knowledge beyond the f(7/2) shell closure and allows us to derive the effective proton and neutron charges in the fp shell near the doubly magic nucleus Ca-48, using large-scale, shell-model calculations. These results indicate an orbital dependence of the core polarization along the fp shell.
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| 7. |
- Büntgen, Ulf, et al.
(författare)
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The influence of decision-making in tree ring-based climate reconstructions
- 2021
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Tree-ring chronologies underpin the majority of annually-resolved reconstructions of Common Era climate. However, they are derived using different datasets and techniques, the ramifications of which have hitherto been little explored. Here, we report the results of a double-blind experiment that yielded 15 Northern Hemisphere summer temperature reconstructions from a common network of regional tree-ring width datasets. Taken together as an ensemble, the Common Era reconstruction mean correlates with instrumental temperatures from 1794–2016 CE at 0.79 (p < 0.001), reveals summer cooling in the years following large volcanic eruptions, and exhibits strong warming since the 1980s. Differing in their mean, variance, amplitude, sensitivity, and persistence, the ensemble members demonstrate the influence of subjectivity in the reconstruction process. We therefore recommend the routine use of ensemble reconstruction approaches to provide a more consensual picture of past climate variability.
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| 8. |
- Pascoal, T. A., et al.
(författare)
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Longitudinal 18F-MK-6240 tau tangles accumulation follows Braak stages
- 2021
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Ingår i: Brain. - : Oxford University Press (OUP). - 0006-8950 .- 1460-2156. ; 144:11, s. 3517-3528
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Tidskriftsartikel (refereegranskat)abstract
- Tracking longitudinal tau tangles accumulation across the Alzheimer's disease continuum is crucial to better understand the natural history of tau pathology and for clinical trials. Although the available first-generation tau PET tracers detect tau accumulation in symptomatic individuals, their nanomolar affinity offers limited sensitivity to detect early tau accumulation in asymptomatic subjects. Here, we hypothesized the novel subnanomolar affinity tau tangles tracer 18F-MK-6240 can detect longitudinal tau accumulation in asymptomatic and symptomatic subjects. We studied 125 living individuals (65 cognitively unimpaired elderly amyloid-β-negative, 22 cognitively unimpaired elderly amyloid-β-positive, 21 mild cognitive impairment amyloid-β-positive and 17 Alzheimer's disease dementia amyloid-β-positive individuals) with baseline amyloid-β 18F-AZD4694 PET and baseline and follow-up tau 18F-MK-6240 PET. The 18F-MK-6240 standardized uptake value ratio (SUVR) was calculated at 90-110 min after tracer injection and the cerebellar crus I was used as the reference region. In addition, we assessed the in vivo18F-MK-6240 SUVR and post-mortem phosphorylated tau pathology in two participants with Alzheimer's disease dementia who died after the PET scans. We found that the cognitively unimpaired amyloid-β-negative individuals had significant longitudinal tau accumulation confined to the PET Braak-like stage I (3.9%) and II (2.8%) areas. The cognitively unimpaired amyloid-β-positive individuals showed greater tau accumulation in Braak-like stage I (8.9%) compared with later Braak stages. The patients with mild cognitive impairment and those who were Alzheimer's dementia amyloid-β-positive exhibited tau accumulation in Braak regions III-VI but not I-II. Cognitively impaired amyloid-β-positive individuals that were Braak II-IV at baseline displayed a 4.6-7.5% annual increase in tau accumulation in the Braak III-IV regions, whereas those who were cognitively impaired amyloid-β-positive Braak V-VI at baseline showed an 8.3-10.7% annual increase in the Braak regions V-VI. Neuropathological assessments confirmed PET-based Braak stages V-VI in the two brain donors. Our results suggest that the 18F-MK-6240 SUVR is able to detect longitudinal tau accumulation in asymptomatic and symptomatic Alzheimer's disease. The highest magnitude of 18F-MK-6240 SUVR accumulation moved from the medial temporal to sensorimotor cortex across the disease clinical spectrum. Trials using the 18F-MK-6240 SUVR in cognitively unimpaired individuals would be required to use regions of interest corresponding to early Braak stages, whereas trials in cognitively impaired subjects would benefit from using regions of interest associated with late Braak stages. Anti-tau trials should take into consideration an individual's baseline PET Braak-like stage to minimize the variability introduced by the hierarchical accumulation of tau tangles in the human brain. Finally, our post-mortem findings supported use of the 18F-MK-6240 SUVR as a biomarker to stage tau pathology in patients with Alzheimer's disease. © 2021 The Author(s) (2021). Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved. For permissions, please email: journals.permissions@oup.com.
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| 10. |
- Gachet, S, et al.
(författare)
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A probabilistic approach to the use of pollen indicators for plant attributes and biomes: an application to European vegetation at 0 and 6 ka
- 2003
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Ingår i: Global Ecology and Biogeography Letters. - 0960-7447. ; 12:2, s. 103-118
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Tidskriftsartikel (refereegranskat)abstract
- Aim This paper presents a probabilistic method for the characterization of pollen taxa using attributes, and for the reconstitution of past biomes. The probabilities are calculated on the basis of European floristic and pollen databases sufficiently large and exhaustive to provide robust estimates. Location The analysis is based on data from approximately 1000 sites throughout Europe. Method We use all the pollen data from the European Pollen Database (EPD), which contains about 50 000 pollen assemblages distributed across Europe and covering the period from the Last Glacial Maximum to the present. Using existing floras, each pollen taxon has been characterized by allocating one or more modes of several attributes, chosen according to the biogeography and phenology of the taxon. With this information, conditional probabilities are defined, representing the chance of a given attribute mode occurring in a given pollen spectrum, when the taxa assemblage is known. The concept of co-occurrence is used to provide a greater amount of information to compensate for difficulties in the identification of pollen grains, allowing a better interpretation when there is little diversity in the pollen assemblage. Results The method has been validated using a dataset of modern samples against existing methods of biome classification and remote sensing data. An application is proposed in which the new method is used to produce biomes for pollen data 6000 years ago. This confirms previous results showing an extension of the deciduous forest to the north, east and south, explained by milder winters in western and northern Europe, and cooler and wetter climate in the Mediterranean region. Conclusion The results show the new method to be efficient, reliable and flexible and to be an improvement over the previous method of biomization. They will be used to test simulations of earth system models running on periods with climate significantly different from the present day, enabling a robust test of the validity of applying these models to the future.
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