Results 1 - 10 of 200605
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[en] Early infarcts are hard to diagnose on non-contrast head CT. Dual-energy CT (DECT) may potentially increase infarct differentiation. The optimal DECT settings for differentiation were identified and evaluated. One hundred and twenty-five consecutive patients who presented with suspected acute ischemic stroke (AIS) and underwent non-contrast DECT and subsequent DWI were retrospectively identified. The DWI was used as reference standard. First, virtual monochromatic images (VMI) of 25 patients were reconstructed from 40 to 140 keV and scored by two readers for acute infarct. Sensitivity, specificity, positive, and negative predictive values for infarct detection were compared and a subset of VMI energies were selected. Next, for a separate larger cohort of 100 suspected AIS patients, conventional non-contrast CT (NCT) and selected VMI were scored by two readers for the presence and location of infarct. The same statistics for infarct detection were calculated. Infarct location match was compared per vascular territory. Subgroup analyses were dichotomized by time from last-seen-well to CT imaging. A total of 80–90 keV VMI were marginally more sensitive (36.3–37.3%) than NCT (32.4%; p > 0.680), with marginally higher specificity (92.2–94.4 vs 91.1%; p > 0.509) for infarct detection. Location match was superior for VMI compared with NCT (28.7–27.4 vs 19.5%; p < 0.010). Within 4.5 h from last-seen-well, 80 keV VMI more accurately detected infarct (58.0 vs 54.0%) and localized infarcts (27.1 vs 11.9%; p = 0.004) than NCT, whereas after 4.5 h, 90 keV VMI was more accurate (69.3 vs 66.3%). Non-contrast 80–90 keV VMI best differentiates normal from infarcted brain parenchyma.
[en] The water chemistry control in Nuclear Power Plants (NPPs) is important at least for the next reasons: structural materials integrity, plant radiation levels, deposits build-up and safety. One of the most important NPP systems is Primary Heat Transport System (PHTS) having in view its role in active zone cooling and heat transfer to steam generators. In PHTS the chemical control is directed to keep chemical parameters within specified limits in order to mitigate the corrosion of the key equipment and related piping, to control the corrosion rate and impurities concentration, such as corrosion and fission products and to minimize activity transport and heat transfer surfaces fouling. By operation in aqueous environment at high temperature and pressure, the structural materials from PHTS are covered with protective oxide films, which maintain the corrosion rate in admissible limits. A lot of potential factors exist, which can degrade the protective films and consequently intensify the corrosion processes. In order to minimize these adverse effects, an optimal water chemistry control and corrosion monitoring program were established. The understanding of the corrosion degradation phenomena that result in failure of some components from PHTS of CANDU NPP necessitates investigation of the structural materials corrosion processes in different conditions of water chemistry and temperature. Water chemistry management in Nuclear Power Plants can then be applied to mitigate the corrosive environments inherent in plant operation. The basis of chemistry control process consists of operational experience, laboratory tests, structural materials corrosion behaviour and the transport and deposition of impurities and corrosion products under operating conditions. To investigate the corrosion process of some structural materials from PHTS (Zr alloys) of CANDU 6 reactor corrosion experiments were performed in autoclaves assembled in by-pass loops of CANDU 6 reactor PHTS Cernavoda Unit#1 This paper presents the results obtained by in-situ monitoring of PHWR water chemistry effect on fuel cladding corrosion, Zircaloy-4. The optical metallographic and scanning electron microscopies, as well as XRD analysis have been used to evaluate the corrosion behaviour of the fuel cladding material, Zircaloy-4 coupons exposed in PHTS autoclaves system. The obtained results allowed us to establish the contribution of the water chemistry on the Zircaloy-4 corrosion behaviour. (author)
[en] The out of core structural material in the primary heat transport system of Indian Pressurized Heavy Water Reactor is Carbon Steel (CS). Prolonged operation of these reactors at high temperature and high pressure leads to the formation of activated corrosion products which get deposited on out-of-core surfaces causing radiation field build up and man-rem problems. Though the corrosion rate of CS is reduced by passive magnetite (Fe3O4) film, the radioactivity transport problem necessitates further reduction in the metal ion release. Metal ion passivation method is used to modify the oxide films to control the base metal corrosion. In this context, experiments were carried out to know the extent of improvement in corrosion resistance of CS with the addition of external metal ions such as Ni2+, Zn2+ and Mg2+ compared to Fe3O4. In addition, the effect of Mg2+ on the surface oxide films formed on Zircaloy-2 and Incoloy-800 were also studied. For CS, all the experiments were carried out in a static autoclave with lithium hydroxide in presence of Ni2+, Zn2+ and Mg2+ ions respectively at 250°C exposed for 96 and 240 hours by hydrothermal method. For Incoloy-800 and Zircaloy-2, experiments were done in a dynamic loop for duration of 7, 21 and 42 days only with magnesium ion. The films were characterized both by surface analytical techniques like Raman and GI-XRD for compositional analysis and also by electrochemical techniques for evaluating corrosion resistance properties. On CS, the films grown in presence of metal ions exhibited a higher polarization resistance compared to its absence by impedance studies. Potentiodynamic anodic polarization studies showed a similarity in corrosion current densities for the films obtained in the absence and presence of metal ions. The calculated thickness of these modified films using Clarke’s method was lower in presence of Zn2+ and Mg2+ ions compared to Ni2+ ions and Fe3O4. From the results, it was inferred that the zinc and magnesium ferrites form a more adherent and compact film compared to Fe3O4 and nickel ferrite. On both Incoloy and Zircaloy, a restructuring of oxide was indicated as a function of time and the corrosion rates and defect densities were found to be significantly lower on Mg2+ incorporated oxides. (author)
[en] Pressurized Heavy Water Reactor (PHWR), CANadian Deuterium-Uranium (CANDU), Operating Experience (OPEX) provides evidence that performing post-refurbishment Primary Heat Transport System (PHTS) Hot Conditioning (HC) with fuel in core presents a risk that the fuel bundles may become coated with iron-based, primarily magnetite and hematite, deposits during the evolution. This OPEX also provide evidence that these deposits remain on the fuel sheath for a period of approximately three to six months into the subsequent operation of the plant before the deposit material is redistributed into the PHTS coolant and removed from the system through the PHTS purification system. Such deposits, while present on the sheath, are thought to contribute to fuel sheath corrosion and impact fuel element heat transfer properties. OPG commissioned a series of laboratory testing to investigate the factors that contribute to the phenomena of fuel sheath deposit formation. These tests included comparative studies of HC evolutions, which emulated recent CANDU post-refurbishment OPEX in a laboratory setting. These investigations provided clarity on the parameters relevant to this adverse condition and on controls that can be implemented to minimize deposition on fuel bundle sheath surfaces. Sensitive parameters and associated controls include; (1) use of a “conventional” HC process as compared to a chelating-agent type HC, that use forms of Ethylenediaminetetraacetic Acid (e.g. Li2EDTA), (2) HC prior to reactor first approach-to-critical (i.e. no fuel heat), (3) maintenance of PHTS pH per current industry expert recommendations, and (4) careful control of other dissolved materials in the PHTS during PHT cold flush. OPEX observations suggest that the surface condition of fuel sheathing may also be a contributing factor related to the probability of deposition. This indicates that fuel sheaths that have been “polished” following tube production may be less susceptible to deposition of magnetite on sheath surfaces during HC. While OPG has considered this observation to be interesting, it was not further investigated, and thus requires validation. (author)
[en] Several countries are planning their first/new research reactor as a key national facility for the development of their nuclear science and technology programmes, including nuclear power. The introduction of a new research reactor in a country requires the establishment of an adequate national infrastructure, covering a wide range of technical areas. This paper briefly describes certain special characteristics of a nuclear power programme which need to be kept in mind by government planners and policy makers before any country embarks on a nuclear energy programme. It also briefly describes the infrastructure and institutions that are required to be built for sustenance of a nuclear energy programme. In the end, it also describes India’s nuclear energy programme. (author)
[en] The Jordan Research and Training Reactor (JRTR) is Jordan’s first critical nuclear facility, owned and operated by the Jordan Atomic Energy Commission (JAEC). The reactor was successfully commissioned in 2016, has obtained its operating license from Jordan’s nuclear regulatory body, and is currently working on optimizing and extending its operation and utilization activities. In this work, prospects of utilizing the JRTR are presented by describing potential utilization applications suitable for the JRTR and of interest to its stakeholders, and afterward, challenges on the way of realizing and implementing those applications are discussed. (author)
[en] The development of new cathode materials with high capacity, good stability, and high safety is important for the future improvement of Li batteries. LiFeBO is considered to be a type of promising electrode materials for Li-ion batteries due to its low cost, high theoretical capacity of 220 mAh/g (about 30% larger than that of LiFePO), low toxicity, and small volume change of 2% during the Li reversible extraction/insertion process. However, its electronic conductivity and rate performance still need further improvement. To optimize the performance of the LiFeBO, Mn, Cr, and Ni doping at Fe site have been studied experimentally, while the effect of minor addition of 3d transition metals on the electronic structure of LiFeBO is rarely investigated. Thus, density functional theory calculations corrected by on-site Coulomb interactions have been conducted to study the crystal structure and electronic property of the LiFeMBO (M = Mn, Co, and Ni) electrode systems. The results indicate that the coordination geometry about Fe in LiFeBO is a distorted trigonal bipyramid with a distortion which can be attributed to a Jahn-Teller effect. The band gap energy of LiFeBO is calculated to be 3.40 eV, which is in reasonable agreement with the previously computed values. The doping at Fe site with Mn cannot reduce the distortion of Jahn-Teller effect, whereas Co doping intensifies Jahn-Teller distortion of the FeO trigonal bipyramid in LiFeBO. Ni substitution is predicted to be able to introduce impurity levels, and the Jahn-Teller distortion degree of the trigonal bipyramid decreased from 11.9 of the FeO to 8.7% of the NiO. Thus, Ni doping is expected to increase stability and the electronic conductivity of the LiFeBO structure.
[en] Herein, the optically induced operation of ZnO-based laser structures is reported, fabricated with plasma-assisted molecular beam epitaxy (PA-MBE) on native ZnO substrate. ZnMgO is used both to confine the optical mode within ZnO waveguide and to form quantum barriers of ZnO quantum wells. The resonator of these devices is defined by reactive ion etching (RIE) with a chlorine/argon plasma. The lowest laser threshold is measured to be approximately 0.4 MW cm at room temperature when excited via the third harmonic of a YAG:Nd (355 nm). It is observed that the mode spacing depends on both the resonator length and the excitation power density, which is explained by introducing plasmonic corrections to the waveguide refractive index. (© 2020 Wiley‐VCH GmbH)
[en] Optical absorption and emission spectra are the important quantifiable properties for CuI as a promising optoelectronic material. Previous research on the sputter deposition of CuI focuses on room-temperature growth. Herein, the effect of growth temperature on the selected optical features of sputtered CuI thin films is investigated. An enhanced visible light transparency and a steeper absorption edge are achieved for CuI thin films by optimizing the growth temperature. The PL intensity ratio of free exciton to defect-related emission increases with increasing substrate temperature. These results suggest a strategy of growth temperature optimization for the enhanced absorption and emission of CuI for advanced optoelectronic applications. (© 2020 Wiley‐VCH GmbH)
[en] In carbonate electrolytes, the organic-inorganic solid electrolyte interphase (SEI) formed on the Li-metal anode surface is strongly bonded to Li and experiences the same volume change as Li, thus it undergoes continuous cracking/reformation during plating/stripping cycles. Here, an inorganic-rich SEI is designed on a Li-metal surface to reduce its bonding energy with Li metal by dissolving 4m concentrated LiNO in dimethyl sulfoxide (DMSO) as an additive for a fluoroethylene-carbonate (FEC)-based electrolyte. Due to the aggregate structure of NO ions and their participation in the primary Li solvation sheath, abundant LiO, LiN, and LiNO grains are formed in the resulting SEI, in addition to the uniform LiF distribution from the reduction of PF ions. The weak bonding of the SEI (high interface energy) to Li can effectively promote Li diffusion along the SEI/Li interface and prevent Li dendrite penetration into the SEI. As a result, our designed carbonate electrolyte enables a Li anode to achieve a high Li plating/stripping Coulombic efficiency of 99.55 % (1 mA cm, 1.0 mAh cm) and the electrolyte also enables a Li||LiNiCoMnO (NMC811) full cell (2.5 mAh cm) to retain 75 % of its initial capacity after 200 cycles with an outstanding CE of 99.83 %. (© 2020 Wiley‐VCH GmbH)