In situ defect annealing of swift heavy ion irradiated CeO2 and ThO2 using synchrotron X‐ray diffraction and a hydrothermal diamond anvil cell

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111991/1/S160057671500477X.pd

Global patient outcomes after elective surgery: prospective cohort study in 27 low-, middle- and high-income countries.

BACKGROUND: As global initiatives increase patient access to surgical treatments, there remains a need to understand the adverse effects of surgery and define appropriate levels of perioperative care. METHODS: We designed a prospective international 7-day cohort study of outcomes following elective adult inpatient surgery in 27 countries. The primary outcome was in-hospital complications. Secondary outcomes were death following a complication (failure to rescue) and death in hospital. Process measures were admission to critical care immediately after surgery or to treat a complication and duration of hospital stay. A single definition of critical care was used for all countries. RESULTS: A total of 474 hospitals in 19 high-, 7 middle- and 1 low-income country were included in the primary analysis. Data included 44 814 patients with a median hospital stay of 4 (range 2-7) days. A total of 7508 patients (16.8%) developed one or more postoperative complication and 207 died (0.5%). The overall mortality among patients who developed complications was 2.8%. Mortality following complications ranged from 2.4% for pulmonary embolism to 43.9% for cardiac arrest. A total of 4360 (9.7%) patients were admitted to a critical care unit as routine immediately after surgery, of whom 2198 (50.4%) developed a complication, with 105 (2.4%) deaths. A total of 1233 patients (16.4%) were admitted to a critical care unit to treat complications, with 119 (9.7%) deaths. Despite lower baseline risk, outcomes were similar in low- and middle-income compared with high-income countries. CONCLUSIONS: Poor patient outcomes are common after inpatient surgery. Global initiatives to increase access to surgical treatments should also address the need for safe perioperative care. STUDY REGISTRATION: ISRCTN5181700

Probing Point Defects in Fluorite-Structured Actinide and Analogue Oxides

Lanthanide and actinide oxides, such as CeO2 [cerium dioxide], ThO2 [thorium dioxide], and UO2 [uranium dioxide], are attractive candidates for various energy-related applications such as nuclear fuel and electrolytes for solid oxide fuel cells owing in part to the resiliency of their bulk structures at room temperature up to near-melting temperatures. These materials exhibit broad regimes of phase stability under various extreme conditions including high temperature, pressure, and/or energetic ion irradiation. Upon modification from external perturbation (e.g., ion irradiation) or chemical changes (e.g., doping or oxidation), these fluorite-structured oxides incorporate large concentrations of point defects, which can agglomerate and result in complex microstructures that can severely impact component performance. The final state of defect arrangements is governed by unique interactions among the various vacancies, lanthanides, actinides, oxygens, and dopant atoms. This work investigates short-range atomic disorder in swift heavy ion-irradiated CeO2 [cerium dioxide] and ThO2 [thorium dioxide], oxidized UO2 [uranium dioxide], and lanthanide-doped UO2 [uranium dioxide] systems in order to understand how changes in local atomic arrangements correlate to bulk structural modifications and degradation of key material properties. Detailed structural analyses revealed that defect complexes, mostly small oxygen clusters, form in all fluorite-structured oxides after high energy ion irradiation, oxidation, and chemical doping. A number of computational studies have shown that these types of defect agglomerates can exhibit diffusion pathways much faster than isolated point defects. Accurate characterization and understanding of defect cluster stability and migration mechanisms will therefore enable better bulk property predictions that are critical to engineering improved fluorite-structured materials for energy applications

Thermal defect annealing of swift heavy ion irradiated ThO2_2

Isochronal annealing, neutron total scattering, and Raman spectroscopy were used to characterize the structural recovery of polycrystalline ThO2 irradiated with 2-GeV Au ions to a fluence of 1 × 1013 ions/cm2. Neutron diffraction patterns show that the Bragg signal-to-noise ratio increases and the unit cell parameter decreases as a function of isochronal annealing temperature, with the latter reaching its pre-irradiation value by 750 °C. Diffuse neutron scattering and Raman spectroscopy measurements indicate that an isochronal annealing event occurs between 275–425 °C. This feature is attributed to the annihilation of oxygen point defects and small oxygen defect clusters

Defect accumulation in swift heavy ion-irradiated CeO2 and ThO2

Neutron total scattering was used to investigate defect accumulation mechanisms in CeO2 and ThO2 irradiated with 2.2 GeV Au ions. Pair distribution function (PDF) analysis was applied to characterize the local structural evolution and irradiation-induced defects as a function of irradiation fluence. CeO2 exhibits a greater amount of disorder than ThO2 under the same irradiation conditions. The local structures of the two materials evolve differently as a function of ion fluence, even if similar defects are produced. The PDF analysis indicates that oxygen dimer and/or peroxide defects with 〈O–O〉 distances of ∼1.45 Å are formed in CeO2, while irradiation-induced defects in ThO2 result in a change in the mean O–Th–O bond angle and a distortion of local ThO8 polyhedra. Understanding how bound oxygen defects, such as peroxide, affect bulk oxygen transport in CeO2 will aid in better predicting and improving properties of fluorite structure materials for fast ion conductor applications

Pain, Quality of Life, and Functional Capacity With Topical Sevoflurane Application for Chronic Venous Ulcers: A Retrospective Clinical Study

Introduction: Chronic venous ulcers (CVU) commonly have poorly controlled pain. Report: Thirty patients older than 65 years of age with painful CVU were reviewed. At the initial visit, cleaning without sevoflurane was performed. Cleaning visits with sevoflurane every 2 days for 1 month were scheduled. The results of subsequent treatment with sevoflurane at the first, second, seventh, and twelfth cleanings were analysed. Pain was measured using a visual analog scale (VAS), quality of life by the Charing Cross Venous Leg Ulcer Questionnaire, and functional capacity by the Barthel Index. Discussion: Initial VAS was 8.8±1.3 points and at the twelfth cleaning VAS was 0.8±1 points (p=.001). Latency time ranged between 2 and 7 m and duration ranged between 8 and 18 h. It improved quality of life (83±14 points before treatment vs. 50±14 at the twelfth cleaning) and functional capacity (82±13.3 before treatment vs. 91±11.6 points at the twelfth cleaning) (p=.001). The safety profile was favourable with mild and self limited local cutaneous adverse effects, including pruritus, erythema, and heat. No systemic toxicity was detected. Topical sevoflurane may be a therapeutic alternative for painful CVU with a fast, intense, and long-lasting analgesic effect. Keywords: Analgesic treatment, Pain, Satisfaction, Sevoflurane, Ulcer

Effects of Grain Size on the Radiation Response of CeO2, ThO2, and UO2

International audienceRadiation stability is often a key limiting factor in performance of fluorite-structured materials and determining their suitability for use in energy-related applications. In an effort to mitigate the effects of radiation, nanostructured materials are of interest as they incorporate high defect sink strengths [Rose et al., Nanostructured Materials (1995), Nita et al., Journal of Nuclear Materials (2004)]. Recently, it has been shown that the response of CeO2, ThO2, and UO3 to highly ionizing radiation is strongly dependent on the material’s redox response [Tracy et al., Nature Communications (2015)]. When exposed to swift heavy ions, cations in the material are subject to changes in valence which drives swelling and microstrain as irradiation-induced defects accumulate. In this work, we present new insights into how crystallite size affects irradiation-induced redox response and defect accumulation in fluorite-structured simple oxides. Using 946 MeV Au ions at the UNILAC accelerator of the GSI Helmholtz Center, we irradiated microcrystalline and nanocrystalline materials of different compositions containing cations known to reduce (CeO2), remain univalent (ThO2), and oxidize (UO2) under ionizing conditions. Irradiated samples were characterized by synchrotron X-ray diffraction/absorption, neutron total scattering with pair distribution function (PDF) analysis, transmission electron microscopy, and Raman spectroscopy. Each composition exhibits a distinct response between microcrystalline and nanocrystalline forms, such as magnitude of volumetric swelling and secondary phase formation, driven mainly by redox processes. PDF analysis reveals small peroxide-like defects in CeO2 and mono- and di-interstitial clusters in UO2. Our findings imply that nanocrystallinity has negative effects on a material’s response to highly ionizing radiation. These results shed more light onto the interplay of particle size and cation redox behavior and their effect on defect production in an important class of materials, an insight that is essential in developing advanced materials for energy-related applications

Probing the Defect Structure in Single-Phase UO2+x Systems.

International audienceOxidation of uranium dioxide (UO2) nuclear fuel occurs under normal operation and is most evident at high burnup levels or during accident conditions. The excess oxygen is incorporated into the fluorite structure and the resulting atomic-scale defect configuration significantly influences important bulk properties such as thermal conductivity and fission gas release. Previous experimental and modelling efforts have proposed distinct oxygen defect cluster configurations; however, most characterization techniques lack sensitivity to the local atomic structure or the oxygen sublattice and the resulting data cannot be used to validate predicted defect clusters. Here, we present results on single-phase UO2+x systems (x = 0.07 and 0.15) combining advanced experimental and modelling techniques to create high fidelity atomistic models of the oxygen defect clusters. In situ high-temperature neutron total scattering measurements with high sensitivity to the oxygen sublattice were performed at the Nanoscale-Ordered Materials Diffractometer (NOMAD) instrument at the Spallation Neutron Source (Oak Ridge National Laboratory). The data acquired at 600 °C and 1000 °C were analyzed via Reverse Monte Carlo modelling techniques which consider both the long- and short-range structures. The analysis reveals evolving behavior as a function of oxygen content with simple clusters in the low O:M regime (UO2.07) and more complex, extended defects for higher oxygen concentrations (UO2.15). Our findings have implications in improving and validating potentials for Molecular Dynamics simulations to advance larger fuel performance codes