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[en] Geophysics is one of the most useful techniques for uranium exploration. It supports the development of geological models through the definition of lithological, structural and alteration characteristics of metallogenic environments under evaluation. With exploration at increasing depths, the traditional radiometric method is no longer effective for uranium exploration. Uranium mineralization is not closely related with observable gravity, magnetic and impedance anomalies. Gravity, magnetic and electromagnetic techniques can be used to survey the subsurface geological background of an area and can be efficient in detecting deeper uranium deposits. The progression and development of geophysical methods, measurement techniques, data processing, computer modelling and inversion have permitted improvements in the field of uranium exploration. It is well known that progress in geophysical methods has contributed to successful field investigations in the exploration for deeper deposits (including uranium). Xu et al. have reviewed the latest advances and developing trends in geophysical and geochemical methods and techniques applied to uranium resources exploration in China. Following this work, this paper summarizes the research carried out by the East China University of Technology during the past decade. This includes 3-D inversion of magnetic data and 3-D electromagnetic methods tested in the Xiazhuang area over granite type uranium deposits and in the Xiangshan area over volcanic type uranium deposits. Results indicate that some of the objectives, including mapping of basement structures, rock interface and lithology recognition, can be achieved.
[en] Full text: Keda Torus eXperiment (KTX) is a medium size reversed field pinch (RFP) machine which has been constructed to study active feedback control of MHD modes, electromagnetic turbulences and plasma wall interaction under different magnetic configurations, such as low safety factor (q) tokamak and reversed field pinch. The variation of magnetic topology in the presence of both external and internal magnetic perturbations will impact on plasma performance. The first plasma of KTX was achieved on August 2015 shortly after the completion of the construction, suggesting sound physics and engineering design and proper fabrication and assembly. A low q tokamak and transient Reversed Field Pinch operation modes have been achieved with the same power supply system. For the tokamak mode, the maximum stored energy in the poloidal field reached 1.6 MJ, which correspond to a flux swing of about 1 Vs. The edge electron density and electron temperature are measured by Langmuir probes. For tokamak discharge, the measured edge electron density can reach 1019/m3, and the electron temperature is around 10 eV. Magnetic fluctuations are measured by edge magnetic probes. The coherency spectra show coherent signal around 10 kHz with a dominant poloidal mode number m = 3. In RFP operation, effort was made to reverse the toroidal field quickly. RFP state on KTX is achieved for a short period of time. The stable RFP state operation mode is now being pursued on KTX. (author)
[en] Characteristics of Ti–6Al–4V (TC4)/Ti–5Al–2Sn–2Zr–4Mo–4Cr (TC17) bonding interface were investigated via electron backscatter diffraction, transmission electron microscopy and high-resolution transmission electron microscopy techniques. Special attention was paid to clarify the recrystallization mechanism at the bonding interface. The original bond line mainly transformed into the α(TC4)/β(TC17) phase boundary, which was characterized by highly disordered lattice. The plastic flow in the vicinity of α(TC4)/β(TC17) PB occurred in the β phase of TC17 via the dislocation motion, resulting in a curved morphology of the α(TC4)/β(TC17) phase boundary. The enhancement of plastic flow in the β phase of TC17 near the α(TC4)/β(TC17) phase boundary contributed to the occurrence of recrystallized β grains.
[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] Seeking nuclear materials that possess a high resistance against particle radiation damage is a long-standing issue. In this work, to reveal the radiation effect on the metallic glasses (MGs), the atomistic structural evolution of MGs induced by particle radiation is investigated, by performing a molecular dynamics simulation. It is found that radiation-induced vacancy-like defects appear in the MG structural model during the collision cascades. However, these defects are transient and unstable that they are fully annihilated. In particular, free volumes which are specific structural characteristics in MGs can annihilate these transient defects. In addition, there is a rearrangement of free volumes that large free volumes change into small ones and are apt to distribute homogeneously in the amorphous model after structural relaxation, so that the problems of radiation-induced structural instability and energy imbalance are solved. This work will shed light on evaluating the structural stability of MGs under particle radiation.
[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] Full text: An e-fishbone frequency jump has been observed on Tore Supra, which is important for the redistribution of energetic electrons and energetic particle losses. E-fishbone periodic frequency jump phenomena are also observed on HL-2A. Soft X-ray tomography shows that the poloidal and toroidal mode numbers are 1/1 and 2/2 with the frequency jump. In this paper we present a theoretical base of the frequency jump in the e-fishbone experiments. It is identified that barely passing electrons are the drive of the e-fishbone, rather than the trapped electrons. The frequency jumps in HL-2A e-fishbone experiments are numerically reproduced. E-fishbone frequency increases with the hot electron energy which is consistent with the experiments. The growth rate of the mode (m = 2, n = 2) is greater than the one of the mode (m = 1, n = 1) in contrast to the pure MHD prediction. The calculated temporal evolutions of the hot electron energy and the kink mode amplitude are periodic which in good agreement with the observed e-fishbone jump cycle. The theory provides an insight on HL-2A and Tore Supra experiments. (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] 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.