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- Andren, Ann, et al.
(author)
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Effects of treatment with oral appliance on 24-h blood pressure in patients with obstructive sleep apnea and hypertension : a randomized clinical trial
- 2013
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In: Sleep and Breathing. - : Springer Science and Business Media LLC. - 1520-9512 .- 1522-1709. ; 17:2, s. 705-712
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Journal article (peer-reviewed)abstract
- Continuous positive airway pressure treatment has been shown to lower blood pressure (BP) in patients with obstructive sleep apnea (OSA). The aims of the present pilot study were to evaluate the potential effects of oral appliance (OA) therapy on BP, to assess various outcome BP measures, and to inform sample size calculation. Seventy-two patients with OSA and hypertension were randomly assigned to intervention with either an OA with mandibular advancement (active group) or an OA without advancement (control group). Before and after 3 months of treatment, the patients underwent nocturnal somnographic registration and 24-h ambulatory BP monitoring. Among the various BP measures, the largest trend toward effect of OA treatment was seen in 24-h mean systolic BP with a 1.8 mmHg stronger BP reduction in the active group compared with controls. A stronger trend toward effect was seen in a subgroup with baseline ambulatory daytime mean systolic BP > 135/85 mmHg where the mean systolic BP fell, on average, 2.6 mmHg. Additional exclusion of patients with baseline apnea hypopnea index (AHI) a parts per thousand currency sign15 gave a significant reduction in mean systolic BP of 4.4 mmHg (P = 0.044) in the active group compared with controls. In patients with OSA and hypertension, OA treatment had a modest trend toward effect on reducing BP. A stronger trend toward treatment effect was seen after excluding patients with normal baseline ambulatory BP. Additional exclusion of patients with baseline AHI a parts per thousand currency sign15 showed a significant treatment effect. Data to inform sample size for an adequately powered randomized study are provided.
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- Costa, Diogo Ribeiro, et al.
(author)
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Coated UN microspheres embedded in UO2 matrix as an innovative advanced technology fuel: Early progress
- 2021
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In: TopFuel 2021 Light Water Reactor Fuel Performance Conference, Santander, Spain, October 24-28, 2021..
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Conference paper (peer-reviewed)abstract
- Uranium nitride (UN)-uranium dioxide (UO2) composites have been proposed as an innovative advanced technology fuel (ATF) option for light water reactors (LWRs). However, the interdiffusion of oxygen and nitrogen during fabrication result in the formation of α-U2N3. A way to avoid this interaction is to coat the UN with a material that is impermeable to oxygen and nitrogen, has a high melting point, high thermal conductivity, and reasonable low neutron cross-section. Among many candidates,refractory metals may be the first option. In this study, we present an early progressresult of fabricating an innovative ATF concept: coated UN microspheres embedded in UO2 matrix. To do so, the following steps are performed: 1) diffusion couple experiments of UN-X-UO2 (X=W, Mo, Ta, Nb, V) to evaluate the interactions between the coating candidates (X) and the fuels; 2) selection of the most promising candidates; 3) use a surrogate material (ZrN microspheres) to develop processes to coat the microspheres with nanopowders: dry and wet methods; 4) coating the UN microspheres with a selected method; 5) finally, sinter a coated UN-UO2 composite using spark plasma sintering (SPS), and compare the results with an uncoated UNUO2 composite sintered at the same SPS conditions (1500 °C, 80 MPa, 3 min,vacuum). The diffusion couple results indicate W and Mo as the most promising candidates, with the wet method showing the smoothest surface. So, dense (~95 %TD) W/UN-UO2 and Mo/UN-UO2 were sintered and the preliminary results show that the tungsten coating was not efficient due to poor adhesion. Conversely, the Mo coating (~15 µm) was efficient against the α-U2N3 formation. Therefore, this early progress indicates the possibility of fabricating an innovative ATF concept using a low cost and potentially applicable coating method.
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| 7. |
- Costa, Diogo Ribeiro, et al.
(author)
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Coated ZrN sphere-UO2 composites as surrogates for UN-UO2 accident tolerant fuels
- 2022
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In: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 567, s. 153845-
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Journal article (peer-reviewed)abstract
- Uranium nitride (UN) spheres embedded in uranium dioxide (UO2) matrix is considered an innovative accident tolerant fuel (ATF). However, the interaction between UN and UO2 restricts the applicability of such composite in light water reactors. A possibility to limit this interaction is to separate the two materials with a diffusion barrier that has a high melting point, high thermal conductivity, and reasonably low neutron cross-section. Recent density functional theory calculations and experimental results on interface interactions in UN-X-UO2 systems (X = V, Nb, Ta, Cr, Mo, W) concluded that Mo and W are promising coating candidates. In this work, we develop and study different methods of coating ZrN spheres, used as a surrogate material for UN spheres: first, using Mo or W nanopowders (wet and binder); and second, using chemical vapour deposition (CVD) of W. ZrN-UO2 composites containing 15 wt% of coated ZrN spheres were consolidated by spark plasma sintering (1773 K, 80 MPa) and characterised by SEM/FIB-EDS and EBSD. The results show dense Mo and W layers without interaction with UO2. Wet and binder Mo methods provided coating layers of about 20 µm and 65 µm, respectively, while the binder and CVD of W methods layers of about 12 µm and 3 µm, respectively.
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| 8. |
- Costa, Diogo Ribeiro, et al.
(author)
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Oxidation of UN/U 2 N 3 -UO 2 composites: an evaluation of UO 2 as an oxidation barrier for the nitride phases
- 2021
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In: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 544
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Journal article (peer-reviewed)abstract
- Composite fuels such as UN-UO2 are being considered to address the lower oxidation resistance of the UN fuel from a safety perspective for use in light water reactors, whilst improving the in-reactor behaviour of the more ubiquitous UO2 fuel. An innovative UN-UO2 accident tolerant fuel has recently been fabricated and studied: UN microspheres embedded in UO2 matrix. In the present study, detailed oxidative thermogravimetric investigations (TGA/DSC) of high-density UN/U2N3-UO2 composite fuels (91-97 %TD), as well as post oxidised microstructures obtained by SEM, are reported and analysed. Triplicate TGA measurements of each specimen were carried out at 5 K/min up to 973 K in a synthetic air atmosphere to assess their oxidation kinetics. The mass variation due to the oxidation reactions (%), the oxidation onset temperatures (OOTs), and the maximum reaction temperatures (MRTs) are also presented and discussed. The results show that all composites have similar post oxidised microstructures with mostly intergranular cracking and spalling. The oxidation resistance of the pellet with initially 10 wt% of UN microspheres is surprisingly better than the UO2 reference. Moreover, there is no significant difference in the OOT (~557 K) and MRT (~615 K) when 30 wt% or 50 wt% of embedded UN microspheres are used. Therefore, the findings in this article demonstrate that the UO2 matrix acts as a barrier to improve the oxidation resistance of the nitride phases at the beginning of life conditions.
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- Costa, Diogo Ribeiro, et al.
(author)
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UN microspheres embedded in UO2 matrix: An innovative accident tolerant fuel
- 2020
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In: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 540
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Journal article (peer-reviewed)abstract
- Uranium nitride (UN)-uranium dioxide (UO2) composite fuels are being considered as an accident tolerant fuel (ATF) option for light water reactors. However, the complexity related to the chemical interactions between UN and UO(2 )during sintering is still an open problem. Moreover, there is a lack of knowledge regarding the influence of the sintering parameters on the amount and morphology of the alpha-U2N3 phase formed. In this study, a detailed investigation of the interaction between UN and UO2 is provided and a formation mechanism for the resulting alpha-U2N3 phase is proposed. Coupled with these analyses, an innovative ATF concept was investigated: UN microspheres and UO2,13 powder were mixed and subsequently sintered by spark plasma sintering. Different temperatures, pressures, times and cooling rates were evaluated. The pellets were characterised by complementary techniques, including XRD, DSC, and SEM-EDS/WDS/EBSD. The UN and UO2 interaction is driven by O diffusion into the UN phase and N diffusion in the opposite direction, forming a long-range solid solution in the UO2 matrix, that can be described as UO2-xNx. The cooling process decreases the N solubility in UO2-xNx, causing then N redistribution and precipitation as alpha-U2N3 phase along and inside the UO2 grains. This precipitation mechanism occurs at temperatures between 1273 K and 973 K on cooling, following specific crystallographic grain orientation patterns. (C) 2020 The Authors. Published by Elsevier B.V.
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- Dahle, Nina, et al.
(author)
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Nondipping blood pressure pattern predicts cardiovascular events and mortality in patients with atherosclerotic peripheral vascular disease
- 2023
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In: Vascular Medicine. - : Sage Publications. - 1358-863X .- 1477-0377. ; 28:4, s. 274-281
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Journal article (peer-reviewed)abstract
- Background: Patients with peripheral vascular disease (PVD) are often underdiagnosed and undertreated. Nocturnal nondipping blood pressure (BP) pattern, as diagnosed by ambulatory BP monitoring (ABPM), is associated with increased cardiovascular risk, but has not been studied in patients with PVD. We aimed to investigate if a nondipping BP pattern predicts cardiovascular events or all-cause death in outpatients with PVD.Methods: Consecutive outpatients with carotid or lower-extremity PVD were examined with 24-hour ABPM (n = 396). Nondipping was defined as a < 10% fall in systolic BP level during night-time. We used Cox regression models adjusting for potential confounders. We also evaluated the incremental prognostic value of dipping status in the COPART risk score. Our primary composite outcome was cardiovascular events or all-cause death.Results: In the cohort (mean age 70; 40% women), 137 events occurred during a 5.1-year median follow-up; incident rate of 7.35 events per 100 person-years. Nondipping was significantly associated with outcome (hazard ratio 1.55, 95% CI 1.07-2.26, p = 0.021) in a fully adjusted model. When adding nondipping to the risk markers in the COPART risk score, the model fit significantly improved (chi(2) 7.91, p < 0.005) and the C-statistic increased from 0.65 to 0.67.Conclusion: In a cohort of outpatients with PVD, nondipping was an independent risk factor for future cardiovascular events or mortality and seemed to be a strong predictor in patients with carotid artery disease but not in lower-extremity PVD. Additional studies are needed to evaluate the clinical utility of ABPM for improved prevention in these high-risk patients. (ClinicalTrials.gov Identifier: NCT01452165)
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