| 61. |
- Sanchez-Gonzalez, A., et al.
(författare)
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Accurate prediction of X-ray pulse properties from a free-electron laser using machine learning
- 2017
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Free-electron lasers providing ultra-short high-brightness pulses of X-ray radiation have great potential for a wide impact on science, and are a critical element for unravelling the structural dynamics of matter. To fully harness this potential, we must accurately know the X-ray properties: intensity, spectrum and temporal profile. Owing to the inherent fluctuations in free-electron lasers, this mandates a full characterization of the properties for each and every pulse. While diagnostics of these properties exist, they are often invasive and many cannot operate at a high-repetition rate. Here, we present a technique for circumventing this limitation. Employing a machine learning strategy, we can accurately predict X-ray properties for every shot using only parameters that are easily recorded at high-repetition rate, by training a model on a small set of fully diagnosed pulses. This opens the door to fully realizing the promise of next-generation high-repetition rate X-ray lasers.
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| 62. |
- Sehgal, B. R., et al.
(författare)
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Assessment of reactor vessel integrity (ARVI)
- 2003
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Ingår i: Nuclear Engineering and Design. - 0029-5493 .- 1872-759X. ; 221:03-jan, s. 23-53
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Tidskriftsartikel (refereegranskat)abstract
- The cost-shared project ARVI (assessment of reactor vessel integrity) involves a total of nine organisations from Europe and USA. The objective of the ARVI Project is to resolve the safety issues that remain unresolved for the melt vessel interaction phase of the in-vessel progression of a severe accident. The work consists of experiments and analysis development. Four tests were performed in the EC-FOREVER Programme, in which failure was achieved in-vessels employing the French pressure vessel steel. The tests were analysed with the commercial code ANSYS-Multiphysics, and the codes SYSTUS+ and PASULA, and quite good agreement was achieved for the failure location. Natural convection experiments in stratified pools have been performed in the SIMECO and the COPO facilities, which showed that much greater heat is transferred downwards for immiscible layers or before layers mix. A model for gap cooling and a set of simplified models for the system codes have been developed. MVITA code calculations have been performed for the Czech and Hungarian VVERs, towards evaluation of the in-vessel melt retention accident management scheme. Tests have been performed at the ULPU facility with organised flow for vessel external cooling. Considerable enhancement of the critical heat flux (CHF) was obtained. The ARVI Project has reached the halfway stage. This paper presents the results obtained thus far from the project.
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| 63. |
- Urban, Edward R., et al.
(författare)
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The importance of bottom-up approaches to international cooperation in ocean science: The iron story
- 2020
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Ingår i: Oceanography. - : The Oceanography Society. - 1042-8275. ; 33, s. 11-15
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- © 2020, Oceanography Society. All rights reserved. In the past decade, several international efforts developed to address urgent societal issues have been identified through, for example, the United Nations 2030 Agenda for Sustainable Development and its associated 17 Sustainable Development Goals and the United Nations Decade of Ocean Science for Sustainable Development (2021–2030). These worthy efforts will bring ocean science research to bear on problems that need attention in the short term. Yet, there is also a continuing need at the international level to support fundamental ocean science and solve methodological issues over the long term. While knowledge needs to be created before it can be applied, national and international science strategy documents often do not mention the need to maintain the health of the basic science enterprise. We argue that international organizations designed to create knowledge must be maintained and strengthened to inform decisions on how to allocate funding for generating knowledge about the ocean versus solving ocean problems. We use the ocean iron cycle as an example of the benefits of using such a “bottom-up” approach to knowledge generation.
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| 64. |
- Van Dorsselaere, J.P., et al.
(författare)
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ASTEC extension to other reactor types than Generation II PWR
- 2008
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Ingår i: Proc. of ERMSAR 2008.
-
Konferensbidrag (refereegranskat)abstract
- The initial IRSN-GRS requirements for the development of the ASTEC European integral codecovered all present and future PWR, VVER and BWR. After 4 years and a half of SARNET activities, theASTEC V1 code is fully applicable to all severe accident scenarios, at power operation, in Gen.II PWR andVVER. Partners performed substantial code assessment tasks on both VVER-440 and 1000 with good resultson validation (such as PACTEL) and benchmarking with other codes on plant sequences.In the frame of preparation of the new series of ASTEC V2 versions that will account for the needs ofevolution expressed by the SARNET partners, the extension to Gen.III PWR is under way. The 1stversionV2.0, planned for march 09, will be applicable to the EPR, in particular its external core-catcher and to newPWR designs with In-Vessel Melt Retention (IVMR), the latter thanks to CEA work. IVS calculations onVVER-440/V213 showed the ASTEC V1 capabilities to evaluate the IVMR possibilities: these capabilitieswill be improved in the future through a coupled analysis of in-vessel corium and cavity cooling circuit.For BWR applications, the KTH ranking of needs of model adaptations was reviewed by GRS. Theseadaptations mainly concern the Reactor Cooling System (RCS) thermal-hydraulics (internal pumps, drier,separator...) and the core degradation (canisters, control rod guide tubes, penetrations in lower head...). Forcore degradation, the scoping application test on the CORA-18 experiment using the current ASTEC V1models (for adaptation to absorber blades and canisters) showed promising results. The GRS benchmark withthe COCOSYS GRS code showed the applicability of the CPA containment module. For ex-vesselphenomena, the only missing model is the formation of a debris bed during corium slump from lower headinto a flooded cavity after lower head failure and its coolability/erosion behaviour with core concreteinteraction under flooded conditions. All other current V1 models can be used, sometimes with minoradaptations or further need of validation, as for iodine behaviour in containment at temperatures up to 1000Kand the possible decomposition of metal iodides to gaseous iodine at these high temperatures in atmosphere.Detailed specifications will be written soon to prepare the development and validation task planned inSARNET2 with the same partners.For CANDU reactors applications, the priority concerns the core degradation due to the peculiarity ofthe vessel geometry (horizontal core, pressure tubes, calandria...). The exploratory plant applications haveshown that all other current models can be used but tests are still necessary to conclude on models of PHT(Primary Heat Transfer) thermal-hydraulics. INR work takes benefit of the AECL knowledge of MAAP4-CANDU models. A significant benefit is foreseen from the BARC (India) work on core degradation modelsin the frame of IRSN-BARC bilateral collaboration.
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| 65. |
- Vogt, N. M., et al.
(författare)
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Interaction of amyloid and tau on cortical microstructure in cognitively unimpaired adults
- 2022
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Ingår i: Alzheimer's and Dementia. - : Wiley. - 1552-5260 .- 1552-5279. ; 18:1, s. 65-76
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: Neurite orientation dispersion and density imaging (NODDI), a multi-compartment diffusion-weighted imaging (DWI) model, may be useful for detecting early cortical microstructural alterations in Alzheimer's disease prior to cognitive impairment. Methods: Using neuroimaging (NODDI and T1-weighted magnetic resonance imaging [MRI]) and cerebrospinal fluid (CSF) biomarker data (measured using Elecsys® CSF immunoassays) from 219 cognitively unimpaired participants, we tested the main and interactive effects of CSF amyloid beta (Aβ)42/Aβ40 and phosphorylated tau (p-tau) on cortical NODDI metrics and cortical thickness, controlling for age, sex, and apolipoprotein E ε4. Results: We observed a significant CSF Aβ42/Aβ40 × p-tau interaction on cortical neurite density index (NDI), but not orientation dispersion index or cortical thickness. The directionality of these interactive effects indicated: (1) among individuals with lower CSF p-tau, greater amyloid burden was associated with higher cortical NDI; and (2) individuals with greater amyloid and p-tau burden had lower cortical NDI, consistent with cortical neurodegenerative changes. Discussion: NDI is a particularly sensitive marker for early cortical changes that occur prior to gross atrophy or development of cognitive impairment. © 2021 the Alzheimer's Association
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| 66. |
- Wang, Baolin, et al.
(författare)
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Microbial communities mediating net methylmercury formation along a trophic gradient in a peatland chronosequence
- 2023
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Ingår i: Journal of Hazardous Materials. - : Elsevier BV. - 0304-3894 .- 1873-3336. ; 442
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Tidskriftsartikel (refereegranskat)abstract
- Peatlands are generally important sources of methylmercury (MeHg) to adjacent aquatic ecosystems, increasing the risk of human and wildlife exposure to this highly toxic compound. While microorganisms play important roles in mercury (Hg) geochemical cycles where they directly and indirectly affect MeHg formation in peatlands, potential linkages between net MeHg formation and microbial communities involving these microorganisms remain unclear. To address this gap, microbial community composition and specific marker gene transcripts were investigated along a trophic gradient in a geographically constrained peatland chronosequence. Our results showed a clear spatial pattern in microbial community composition along the gradient that was highly driven by peat soil properties and significantly associated with net MeHg formation as approximated by MeHg concentration and %MeHg of total Hg concentration. Known fermentative, syntrophic, methanogenic and iron-reducing metabolic guilds had the strong positive correlations to net MeHg formation, while methanotrophic and methylotrophic microorganisms were negatively correlated. Our results indicated that sulfate reducers did not have a key role in net MeHg formation. Microbial activity as interpreted from 16S rRNA sequences was significantly correlated with MeHg and %MeHg. Our findings shed new light on the role of microbial community in net MeHg formation of peatlands that undergo ontogenetic change.
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| 67. |
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