| 1. |
- Sherratt, K., et al.
(författare)
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Predictive performance of multi-model ensemble forecasts of COVID-19 across European nations
- 2023
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Ingår i: eLIFE. - : eLife Sciences Publications Ltd. - 2050-084X. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Methods: We used open-source tools to develop a public European COVID-19 Forecast Hub. We invited groups globally to contribute weekly forecasts for COVID-19 cases and deaths reported by a standardised source for 32 countries over the next 1–4 weeks. Teams submitted forecasts from March 2021 using standardised quantiles of the predictive distribution. Each week we created an ensemble forecast, where each predictive quantile was calculated as the equally-weighted average (initially the mean and then from 26th July the median) of all individual models’ predictive quantiles. We measured the performance of each model using the relative Weighted Interval Score (WIS), comparing models’ forecast accuracy relative to all other models. We retrospectively explored alternative methods for ensemble forecasts, including weighted averages based on models’ past predictive performance.Results: Over 52 weeks, we collected forecasts from 48 unique models. We evaluated 29 models’ forecast scores in comparison to the ensemble model. We found a weekly ensemble had a consistently strong performance across countries over time. Across all horizons and locations, the ensemble performed better on relative WIS than 83% of participating models’ forecasts of incident cases (with a total N=886 predictions from 23 unique models), and 91% of participating models’ forecasts of deaths (N=763 predictions from 20 models). Across a 1–4 week time horizon, ensemble performance declined with longer forecast periods when forecasting cases, but remained stable over 4 weeks for incident death forecasts. In every forecast across 32 countries, the ensemble outperformed most contributing models when forecasting either cases or deaths, frequently outperforming all of its individual component models. Among several choices of ensemble methods we found that the most influential and best choice was to use a median average of models instead of using the mean, regardless of methods of weighting component forecast models.Conclusions: Our results support the use of combining forecasts from individual models into an ensemble in order to improve predictive performance across epidemiological targets and populations during infectious disease epidemics. Our findings further suggest that median ensemble methods yield better predictive performance more than ones based on means. Our findings also highlight that forecast consumers should place more weight on incident death forecasts than incident case forecasts at forecast horizons greater than 2 weeks.
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| 2. |
- Atac, A, et al.
(författare)
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Single-step link of the superdeformed band in Eu-143
- 1996
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Ingår i: ZEITSCHRIFT FUR PHYSIK A-HADRONS AND NUCLEI. - : SPRINGER VERLAG. - 0939-7922. ; 355:4, s. 343-344
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- A discrete gamma-ray transition with an energy of 3360.6 keV deexciting the second lowest SD state in Eu-143 has been discovered. It carries 3.2 % of the full intensity of the band and feeds into a nearly spherical state which is above the I = 35/2((+)),
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| 3. |
- Axelsson, A, et al.
(författare)
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Single-step link from yrast SD band in Eu-143
- 1997
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Ingår i: PROGRESS IN PARTICLE AND NUCLEAR PHYSICS. - : PERGAMON PRESS LTD. - 0146-6410. ; 38, s. 51-52
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- A discrete gamma-ray transition from the yrast SD band to the region of near-yrast discrete normal-deformed states has been identified in Eu-143. It has an energy of 3360.6 keV and an intensity corresponding to 3.2% of the full intensity of the SD band an
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| 4. |
- Bandini, G., et al.
(författare)
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Safety Analysis Results of Representative DEC Accidental Transients for the ALFRED Reactor
- 2013
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Konferensbidrag (refereegranskat)abstract
- The conceptual design of the Advanced Lead Fast Reactor European Demonstrator (ALFRED) is under development within the LEADER project to meet the safety objectives of Gen IV nuclear energy systems. This paper presents the main results of the safety analysis for beyond design basis conditions, namely design extension conditions (DEC), which include the failure of prevention and mitigation systems, like the reactor scram in the so called unprotected transients. The main objective of this analysis is to evaluate the impact of the core and plant design features on the intrinsic safety behaviour of the ALFRED reactor. Several computer codes: SIM LFR, RELAP5, CATHARE, SPECTRA and TRACE are applied to evaluate the consequences of representative unprotected accident scenarios such as Loss of Flow, Loss of Heat Sink and Reactivity initiated accidents. Additionally, the consequences of steam generator tube rupture and partial sub assembly flow blockage events are assessed by means of appropriate fluid dynamic codes.
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| 5. |
- Wallenius, Janne, 1968-, et al.
(författare)
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Application of burnable absorbers in an accelerator-driven system
- 2001
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Ingår i: Nuclear science and engineering. - 0029-5639 .- 1943-748X. ; 137:1, s. 96-106
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Tidskriftsartikel (refereegranskat)abstract
- The application of burnable absorbers (BAs) to minimize power peaking, reactivity loss, and capture-to-fission probabilities in an accelerator-driven waste transmutation system has been investigated. Boron-IO-enriched B4C absorber rods were introduced into a lead-bismuth-cooled core fueled with transuranic (TRU) discharges from light water reactors to achieve the smallest possible power peakings at beginning-of-life (BOL) subcriticality level of 0.97 Detailed Monte Carlo simulations show that a radial power peaking equal to 1.2 at BOL is attainable using a four-zone differentiation in BA content. Using a newly written Monte Carlo burnup code, reactivity losses were calculated to be 640 pcm per percent TRU burnup for unrecycled TRU discharges. Comparing to corresponding values in BA-free cores, BA introduction diminishes reactivity losses in TRU-fueled subcritical cores by similar to 20%. Radial power peaking after 300 days of operation at 1200-MW thermal power was0.92, which appears to be acceptable, with respect to limitations in cladding and fuel temperatures. In addition, the else of BAs yields significantly higher fission-to-capture probabilities in even-neutron-number nuclides. Fission-to-absorption probability ratio for Am-241 equal to 0.33 was achieved in the configuration studied. Hence, production of the strong alpha-emitter Cm-242 is reduced, leading to smaller fuel-swelling rates and pin pressurization. Disadvantages following BA introduction such as increase of void worth and decrease of Doppler feedback in conjunction with small values of beta (eff), need to be addressed by derailed studies of subcritical core dynamics.
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