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[en] Turbulence-driven plasma accelerators produced by magnetized accretion disks around black holes are proposed as the mechanism mainly responsible for observed cosmic ray protons with ultra high energies 1019-1021 eV. The magnetized disk produces a voltage comparable to these cosmic ray energies. Here we present a Poynting model in which this voltage provides all of the energy to create the jet-like structures observed to be ejected from accretion disks, and this voltage also accelerates ions to high energies at the top of the expanding structure. Since the inductive electric field E = -v x B driving expansion has no component parallel to the magnetic field B, ion acceleration requires plasma wave generation - either a coherent wave accelerator as recently proposed, or instability-driven turbulence. We find that turbulence can tap the full inductive voltage as a quasi-steady accelerator, and even higher energies are produced by transient events on this structure. We find that both MHD modes due to the current and ion diffusion due to kinetic instability caused by the non-Maxwellian ion distribution contribute to acceleration. We apply our results to extragalactic giant radiolobes, whose synchrotron emissions serve to calibrate the model, and we discuss extrapolating to other astrophysical structures. Approximate calculations of the cosmic ray intensity and energy spectrum are in rough agreement with data and serve to motivate more extensive MHD and kinetic simulations of turbulence that could provide more accurate cosmic ray and synchrotron spectra to be compared with observations. A distinctive difference from previous models is that the cosmic ray and synchrotron emissions arise from different parts of the magnetic structure, thus providing a signature for the model
[en] The Sulfur-Iodine (S-I) cycle has been considered as one of the efficient and promising thermochemical water-splitting cycles for hydrogen production using nuclear energy. However, the catalytic SO3 decomposition process in the S-I cycle demands high temperature heat (>800°C). Existing nuclear reactors cannot provide such heat for SO3 decomposition. AECL proposed a direct resistive heating concept to compensate for the requirement of high temperature heat. An experimental program was established at AECL to demonstrate the concept and to develop reliable catalyst structures for SO3 decomposition. Due to the high temperature and harsh chemical environment, Hastelloy C-276 was selected as the material for the heating element and reactor. The catalyst was directly applied on the surface of an electrical heating element. SO3 was produced online from H2SO4 in a pre-heated vessel. The SO3 decomposition percentage was determined using the measured O2 concentration in the exit gas stream. The results showed that SO3 decomposition can be successfully achieved with the direct-resistive heating method. As much as 90% of the initial SO3 was decomposed under the experimental conditions explored. The Pt-based catalyst performed better than the Fe-based catalyst in the low temperature region (<700°C). The effect of carrier gas flow on SO3 decomposition was also considered. (author)
[en] Pressure suppression pool is an important element of BWR containment. It serves as a heat sink and steam condenser to prevent containment pressure buildup during loss of coolant accident or safety relief valve opening during normal operations of a BWR. Insufficient mixing in the pool, in case of low mass flow rate of steam, can cause development of thermal stratification and reduction of pressure suppression pool capacity. For reliable prediction of mixing and stratification phenomena validation of simulation tools has to be performed. Data produced in POOLEX/PPOOLEX facility at Lappeenranta University of Technology about development of thermal stratification in a large scale model of a pressure suppression pool is used for GOTHIC lumped and distributed parameter validation. Sensitivity of GOTHIC solution to different boundary conditions and grid convergence study for 2D simulations of POOLEX STB-20 experiment are performed in the present study. CFD simulation was carried out with FLUENT code in order to get additional insights into physics of stratification phenomena. In order to support development of experimental procedures for new tests in the PPOOLEX facility lumped parameter pre-test GOTHIC simulations were performed. Simulations show that drywell and wetwell pressures can be kept within safety margins during a long transient necessary for development of thermal stratification. (au)
[en] Significant improvement of plasma confinement in the Madison Symmetric Torus reversed field pinch (RFP) has been routinely achieved by applying an inductive electric field at the plasma boundary in the direction parallel to the equilibrium magnetic field at the plasma edge. An auxiliary edge current is driven by this electric field with the goal of replacing the dynamo-driven current and modifying the parallel current profile to reduce current-driven instabilities. This current-drive technique is called pulsed parallel current drive (PPCD) in RFP. During PPCD plasma fluctuations are reduced everywhere resulting in tokamak-like confinement parameters, while the edge density profile steepens significantly and plasma beta increases. A steep edge plasma pressure profile, a relatively high plasma beta and a strong unfavourable curvature of equilibrium magnetic field near the edge in RFP could excite pressure-driven fluid turbulence near the edge and worsen plasma confinement, opposite to the experimental observations. In this study stability analysis of edge pressure gradient driven ideal modes in standard-like and in PPCD-like plasma equilibria is performed. An ideal magnetohydrodynamic plasma model in cylindrical RFP equilibrium with a step function plasma pressure profile and a vacuum layer between the plasma boundary and the conducting shell is used. Standard-like and PPCD-like plasma equilibria in the model are defined by the direction of the surface current at the plasma-vacuum interface. The results show that while in standard-like equilibrium the edge pressure gradient driven modes are highly unstable in this model, the transition to PPCD-like equilibrium completely stabilizes these modes. The modes stabilization is primarily due to strengthening of magnetic shear at the location of the pressure gradient during the drive and due to the proximity of this location to the conducting wall. This stabilization mechanism is not specific to RFPs, making PPCD a general method of stabilization of the edge pressure gradient driven instabilities which could be applied in other magnetic confinement systems. Application of PPCD to stabilize the edge localized modes in tokamaks is proposed.
[en] An immunodipstick assay with a lateral flow strip was developed for fast screening of food for aflatoxin B1 (AFB1) using the respective monoclonal antibody immobilized on nanoparticles with a silver core and a gold shell (AgAu) as detection reagent. The membrane-based immunodipstick consisted of a test line containing AFB1 conjugated to bovine serum albumin, and a control line with goat anti-mouse IgG. One to two colored lines are formed on the membrane by using the red AgAu nanoparticles coated with anti-AFB1 as signaling reagents. Under optimal conditions, the dipstick exhibits a lower visual detection limit of 0. 1 ng mL-1 of AFB1. Compared to the use of pure gold nanoparticles, the AgAu nanoparticles strongly enhance the sensitivity of the assay, and the reproducibility and stability are comparable. The assay was evaluated with naturally contaminated samples including rice, wheat, sunflower, cotton, chillies, and almonds, and a good correlation was found with data obtained with a commercially available enzyme-linked immunosorbent assay. The simple and non-instrumental dipstick method may further be extended to the screening of other mycotoxins in food. (author)
[en] An algorithm suitable for numerical solution of linear eigenmode problems in resistive magnetohydrodynamics (MHD) and two-fluid MHD models without prior approximations is presented. For these plasma models, sets of equations suitable for numerical solution are derived and the details of the algorithm of this solution are given. The algorithm is general and is suitable for solution of boundary (eigenmode) problems for different plasma configurations. It is most effective, however, in one-dimensional models since the grid size has to be sufficiently small in order to resolve the tearing layer together with the scale of the size of the plasma. The technique is applied for solving for tearing eigenmodes in reversed field pinch (RFP) -like plasma in plane geometry. Results of resistive MHD and two-fluid models are compared in this case, showing that the two-fluid effects on tearing modes in RFPs are sizable
[en] This work pertains to the research program on Containment Thermal-Hydraulics at KTH. The objective is to evaluate and improve performance of methods, which are used to analyze thermal-hydraulics of steam suppression pools in a BWR plant under different abnormal transient and accident conditions. As a passive safety system, the function of steam pressure suppression pools is paramount to the containment performance. In the present work, the focus is on apparently-benign but intricate and potentially risk-significant scenarios in which thermal stratification could significantly impede the pool's pressure suppression capacity. For the case of small flow rates of steam influx, the steam condenses rapidly in the pool and the hot condensate rises in a narrow plume above the steam injection plane and spreads into a thin layer at the pool's free surface. When the steam flow rate increases significantly, momentum introduced by the steam injection and/or periodic expansion and shrink of large steam bubbles due to direct contact condensation can cause breakdown of the stratified layers and lead to mixing of the pool water. Accurate prediction of the pool thermal-hydraulics in such scenarios presents a computational challenge. Lumped-parameter models have no capability to predict temperature distribution of water pool during thermal stratification development. While high-order-accurate CFD (RANS, LES) methods are not practical due to excessive computing power needed to calculate 3D high-Rayleighnumber natural circulation flow in long transients. In the present work, a middleground approach is used, namely CFD-like model of the general purpose thermalhydraulic code GOTHIC. Each cell of 3D GOTHIC grid uses lumped parameter volume type closures for modeling of various heat and mass transfer processes at subgrid scale. We use GOTHIC to simulate POOLEX/PPOOLEX experiment, in order to (a) quantify errors due to GOTHIC's physical models and numerical schemes, and (b) propose necessary improvements in GOTHIC sub-grid scale modeling. The study performed on thermal stratification in a water pool indicates that GOTHIC CFD-like model is fit for reactor applications in complex fluidphysics scenarios that avoids both over-simplification (as in single lumpedparameter model) and over-complication (as in CFD models). However, simulation of direct steam injection into a subcooled pool cannot be predicted reliably with the existing models. Thus we develop 'effective heat source' and 'effective momentum' approaches, and provide feasibility study for the prediction of thermal stratification and mixing in a BWR pressure suppression pool. The results are encouraging and further activity on the development and implementation of the proposed models in GOTHIC is currently underway. (Author)
[en] We present in the poster the status of an R and D program towards the goal of an ultra-low-energy germanium (ULEGe) detector at threshold of 100 eV with an active target mass on the order of 1 kg and a background near threshold at the range of 1 event/kg-keV-day. The scientific objectives include the studies of neutrino-nucleus coherent scattering and neutrino magnetic moments, as well as WIMP dark matter searches at the low WIMP mass range. Such detectors would also have potential implications in reactor monitoring for security purposes. A threshold of 220 eV has been demonstrated with a prototype 4-channel ULEGe array with a total mass of 20 g. Competitive limits have been derived for WIMP-nucleon couplings for WIMPs with mass less than 10 GeV. Scale-up plans are described.
[en] This study aimed to characterize the nanostructures in individual calcium phosphate (CP) splats deposited by thermal spray processes. The CP splats were fabricated using both plasma spraying and high velocity oxy-fuel (HVOF) techniques. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) were employed for observing the nanostructures. A nanostructure with ∼30 nm grains within the CP splats was revealed. This is consistent with the nanostructures exhibited within the CP coating. The present results also further confirmed that hydroxyapatite (HA) decomposition mainly occurred within the melted part of the sprayed particles. Furthermore, after 2 days' incubation of the splats in the culture medium, the osteoblast cells have already very well attached and proliferated on the coating. The nanostructures are capable of enhancing the proliferation of the osteoblast cells