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[en] Full text: The Keda torus experiment (KTX) is a new built middle-size reversed field pinch (RFP) device at the University of Science and Technology of China. After the long time conditioning, the favourable wall condition is achieved for implementing experiment on KTX. At present, the maximum plasma current can reach 200 kA, the discharge length is beyond 20 ms and the duration of typical reversed field pinch state is 2:0 ms. The diagnostics on KTX has been greatly developed: 1) Total number of DAQ channel has been upgraded to 960; 2) Terahertz interferometer has been upgraded to 7 chords to obtain density and current profiles; 3) Thomson scattering with 3 J laser is undergoing commissioning; 4) 3D Langmuir probe system has been developed for the electromagnetic turbulence measurement; 5) 3D double-foil soft X-ray diagnostics are mounted on two poloidal sections for 3D MHD research; 6) Edge capacitive probe has been installed for the radial electrical field measurement; 7) Multichannel spectrograph system has been built for detecting impurities of carbon and oxygen. After the wall condition improvement and diagnostics upgrade, many early research such as the 3D RFP physics and electromagnetic turbulence, etc., have been conducted on KTX. The forward scattering is observed by the interferometer system which shows the potential for turbulence research with wider spectrum after improving the beam size and acceptance angle of the diagnostic beam through plasma. The research on MHD activities related with 3D RFP physics on KTX is intensely carried out with the capability upgrade of magnetic field measurement, soft X-ray tomography and high-speed visible imaging system. The electromagnetic turbulence is tentatively investigated on KTX. The 3D spectra characters of electromagnetic turbulence are firstly measured with classical two-point technique by the 3D Langmuir probe arrays, particularly in the small wavenumber range, providing the new prospect of electromagnetic turbulence in RFP plasmas. The confinement improvement of turbulence suppression is achieved in biasing electrode experiment. The resistive MHD modelling of QSH state using NIMROD is setup in the KTX regimes. In the next step, higher performance plasma of KTX with larger plasma current, higher temperature and longer energy confinement time is expected with the capacity upgrade in the second phase. (author)
[en] Highlights: • An experimentally validated computer model has been implemented in User Define Functions. • The validated model is used for a numerical study of CLC using CaSO4 as oxygen carrier and H2 as fuel. • Effects of mole fraction of CaS, temperature, fuel superficial feeding velocity were discussed. • The fuel feeding velocity has significant effect on the flow and conversion performance. • Operating temperature mainly affects the fuel conversion. - Abstract: Due to the severity of the worldwide climate change problem and the ocean acidification problem, chemical looping combustion (CLC) technology is studied worldwide by researchers in order to meet the urgency of carbon emission reduction after its concept has been put forward. An experimentally validated computer model has been implemented in Ansys-Fluent code with the most appropriate kinetic model implemented in User Define Functions. The validated model has been used to carry out a numerical study on a model fuel reactor using CaSO4 as oxygen carrier and H2 as fuel; is conducted in the present work. Effects of mole fraction of CaS, operating temperature, superficial feeding velocity magnitude of fuel and the diameter of oxygen carrier particles were discussed. The results indicate that the superficial feeding velocity of gaseous fuel has significant effects on the flow condition with fuel reactor and conversion performance, while operating temperature mainly affects the fuel conversion. The effects of particle diameter on flow condition within FR are obvious but insignificant on conversion performance of fuel. The mole fraction of CaS has the least effect among these three parameters. Several velocity distributions are also studied. The rectangle-trianble distributor results in better bubbles distributions, but the gain of higher fuel conversion rate is insignificant due to the low chemical activity of OC used in this study.
[en] A method was developed to recognize anatomical site and image acquisition view automatically in 2D X-ray images that are used in image-guided radiation therapy. The purpose is to enable site and view dependent automation and optimization in the image processing tasks including 2D-2D image registration, 2D image contrast enhancement, and independent treatment site confirmation. The X-ray images for 180 patients of six disease sites (the brain, head-neck, breast, lung, abdomen, and pelvis) were included in this study with 30 patients each site and two images of orthogonal views each patient. A hierarchical multiclass recognition model was developed to recognize general site first and then specific site. Each node of the hierarchical model recognized the images using a feature extraction step based on principal component analysis followed by a binary classification step based on support vector machine. Given two images in known orthogonal views, the site recognition model achieved a 99% average F1 score across the six sites. If the views were unknown in the images, the average F1 score was 97%. If only one image was taken either with or without view information, the average F1 score was 94%. The accuracy of the site-specific view recognition models was 100%.
[en] In theory, the influence of spin-orbit interaction on the electron spin transport in inorganic semiconductors was discussed, which was compared with that of organic semiconductors. Results reveal that the internal mechanism of spin precession in inorganic semiconductor is different from that of the organic semiconductor, while the influence of the spin-orbit interaction on the carrier spin transport is same. (paper)
[en] In this paper, we present the phonon dispersion curves of Gallium arsenide (GaAs) at different electronic temperatures. Based on the phonon spectra, we further investigated the thermodynamic properties of GaAs under intense electronic excitation. The phonon entropy, phonon heat capacity and phonon contribution to the Helmholtz free energy and the internal energy as functions of temperature at different electronic temperatures are calculated. A sudden change in the phonon entropy-temperature curve from Te = 1.25 to 1.5 eV provides an indication of GaAs undergoing a phase transition from a solid to a liquid. This can be considered as collateral evidence for the non-thermal melting of GaAs under electronic excitation.
[en] Proton exchange membrane (PEM) electrolysis is the process of cracking water into hydrogen and oxygen using a PEM electrolyzer. The PEM electrolyzer consists of a PEM, bipolar plates, insulators and end plates. In this study, a PEM electrolyzer is designed and developed for its application in the nuclear industry for tritium removal using the catalytic exchange electrolysis process. Tyne, in collaboration with CNL, has designed a tritium-compatible PEM electrolyzer with specially designed 20.3 cm active diameter electrodes which can withstand tritium better than ordinary Nafion® and with enhanced safety features. Electrochemical and hydrodynamic models are used in the design stage to determine various design parameters. A prototype with 1 Nm3/hr design capacity is built and tested with Nafion® N-117. The polarization curve is experimentally determined at ambient temperature and pressure. The results showed that the required single cell potential is 3 V at 1.0 A/cm2. As a second phase of the electrolyzer development, tritium-compatible membrane, specifically developed for tritium application at CNL, was soaked in tritiated water for 3 months and then detritiated for several months. The detritiated membrane has been then tested in a smaller unit. Compared to the soaked Nafion® membranes the specially designed and developed tritium-compatible membranes perform better and thus are to be used in final electrolyzer assembly. (author)
[en] A coherent mode is detected by electron cyclotron emission imaging (ECEI) diagnostic in the pedestal region during ELM-free phase and inter-ELM phase on the Experimental Advanced Super-conducting Tokamak (EAST). In the normal high confinement regime (H-mode) with co-current neutral beam injection (NBI), the coherent mode grows a few milliseconds after L-H transition, and the mode frequency downshifts from about 45 kHz to 15 kHz lasting for about 100 ms before the first ELM crash. It is obvious to say that the mode rotates in the electron diamagnetic direction in the laboratory frame through ECE imaging. Ballooning-like mode structure is identified. The estimated poloidal mode number is m > 25, and toroidal mode number is n > 5 for the local safety factor q ∼ 5. Wave length of the mode increases until the mode saturates, which is consistent with the result that the estimated poloidal mode number decreases. Characteristics of the mode during inter-ELM phase are similar to that during ELM free phase. (author)
[en] Highlights: • A novel non-isothermal creep aging (NICA) process is proposed to improve sheet metal forming efficiency. • Appropriate heating-cooling rate is conducive to obtain desired creep deformation and material properties. • The time consumption in optimized NICA process is about half of that in conventional creep aging process. • In NICA, the precipitates formed in heating will be dissolved nearby the peak temperature and re-precipitated in cooling. - Abstract: To shorten production period and reduce manufacturing cost of high strength aluminum alloy integral panel components, a novel non-isothermal creep age forming (CAF) technology was developed. Taking an Al-Zn-Mg-Cu alloy as the case material, the non-isothermal creep aging (NICA) behavior and the conventional isothermal creep aging (ICA) behavior were comparatively investigated. The corresponding creep deformations, material performance variations and precipitate microstructure evolutions were studied by creep aging tests, mechanical property and corrosion resistance tests, and transmission electron microscope (TEM) and scanning electron microscope (SEM) characterizations. Unlike the ICA which contains short heating and cooling stages and long holding stage, the NICA only has heating and cooling stages, viz., the alloy is heated slowly and the cooling stage begins immediately when reaching the peak temperature. In the NICA process, the precipitates nucleate and grow up in the first half of heating stage, resulting in the reduction of creep rate and enhancement of mechanical strength. The coarsening of precipitates occurs in the second half of heating stage, elevating the creep rate and significantly improving the corrosion resistance. Nearby the peak temperature, the primary precipitates partially dissolve, and the creep rate, mechanical strength and corrosion resistance decrease. Distinctive from the ICA process, a secondary precipitation phenomenon takes place in the cooling stage of NICA, leading to the recovery of high mechanical strength. The higher heating-cooling rate (1 °C/min) is not beneficial to accumulating creep deformation in the shorter creep aging period, while the lower one (0.25 °C/min) causes the loss of mechanical strength due to the excessive dissolution of precipitates. The moderate heating-cooling rate (0.5 °C/min) can lead to larger creep deformation, better mechanical properties and more satisfactory corrosion resistances in the NICA treated alloy, reaching 87.0% of creep strain, 105.7% of yield strength and 97.9% of electric conductivity in the ICA treated alloy. It is worth noting that the time consumption of the optimal NICA process is only 52.9% of the ICA process.
[en] Highlights: • The novel TIG–MIG hybrid welding of Mg and steel has not been reported before. • The joints are weld-brazed with different thickness Cu interlayer. • Microstructures and strengthen mechanisms of different thickness Cu interlayer are different. • The strength with 0.1 mm thickness was improved by 47% compared to that with 0.02 mm thickness. - Abstract: The joining of ferritic stainless steels and magnesium alloys is light and economic for weight reduction of automobiles. Unlike previous conventional welding method, a novel TIG–MIG hybrid welding is applied for the joint successfully in this study. The melted Mg weld metal wets the ferritic stainless steels surface to form a brazed Mg–Cu to steel connection when the interlayer thickness is 0.02 mm. When the interlayer thickness is 0.1 mm, the intermetallic compounds transition layer determined the tensile-shear strength of joints. Intermetallic compounds transition layer has been found in the 0.1 mm thick interlayer joints and no particle has been found in the 0.02 mm thick interlayer joints. Based on the analysis of microstructure and properties, joining and strengthen mechanisms of the joint were discovered. As the thickness of the Cu interlayer increases, the joining mechanism changed. The joining and strengthen mechanisms are mainly determined by the thickness of the interlayer. The tensile-shear strength of 0.1 mm thickness Cu interlayer joints is improved by 47% compared to 0.02 mm Cu.
[en] The natural aging (NA) behaviors within 24 h of 7050 (Al-Zn-Mg-Cu) and 5A90 (Al-Mg-Li) aluminum (Al) alloys are investigated comparatively. The strikingly different evolution rules of mechanical properties and microstructures of the above two materials are characterized using tensile strength tests and high-resolution transmission electron microscopy (HRTEM), then the mechanisms are revealed based on the analysis of differential scanning calorimetry (DSC) and the calculation of precipitation activation energy. It is found that the NA rate of 7050 Al alloy is pronounced in the initial stage (after quenching), and decreases dramatically from 0 h to 20 h of NA, resulting in remarkable evolution of the microstructures and mechanical properties. In contrary, 5A90 Al alloy is stable and the effect of NA is not evident. DSC analysis indicates that the activation energy of the initial precipitate (GP zones) for 7050 Al alloy is nearly 74.3 KJ/mol, while that of the initial precipitate (δ' phase) for 5A90 Al alloy is nearly 103.6 KJ/mol. Owing to the low activation energy, acicular GP zones precipitate in the matrix of 7050 Al alloy within the first 4 h of NA, causing a dramatic increase in strength. The precipitates continue to grow with increasing aging time, albeit at a slower rate and with reduced influence on mechanical strength. Whereas, the strength of the 5A90 Al alloy remains hardly changed due to the higher activation energy. It is noted that, for 7050 Al alloy, the NA induced decreasing of the solute atomic concentration makes the initial remarkable Portevin-Le Chatelier (PLC) effect weaken gradually with aging time. While for the 5A90 Al alloy, the PLC effect remains little changed all the time since NA phenomenon does not occur in this alloy. It is recommended that the as-quenched 7050 Al alloys should be exposed at room temperature for more than 20 h or refrigerated before practical processing.