分类: 核科学技术 >> 核科学技术其他学科 分类: 物理学 >> 核物理学 提交时间: 2024-02-28
摘要: Ferritic/martensitic (F/M) steels have been widely used as structural material for thermal and nuclear power plants. However, it is susceptible to intergranular damage in service conditions, which is expected to be critical issues. In order to improve the intergranular damage resistance of F/M steel, thermomechanical process (TMP) was employed to achieve a grain boundary engineering (GBE) microstructure in a kind of F/M steel P92 in this study. TMP, including cold rolling to 6%, 9%, and 12% thickness reduction, respectively, followed by austenization at 1323 K for 40 min plus tempering at 1053 K for 45 min, were applied on as-received (AR) P92 steel. Both prior austenite grain (PAG) size, prior austenite grain boundary character distribution (GBCD), and the connectivity of prior austenite grain boundaries (PAGBs) were investigated. Compared with AR specimen, the PAG size does not change significantly. The fraction of coincident site lattice boundaries (CSLBs, 3 ≤ Σ ≤ 29) and Σ3n boundaries along PAGBs decreases with increasing reduction ratio due to the recrystallization fraction increases with increasing reduction ratio. The PAGBs connectivity of the 6%-deformed specimen deteriorates compared with that of AR specimen slightly. Moreover, the potentiodynamic polarization studies revealed that the intergranular damage resistance of studied steel could be improved by enhancing the fraction of CSLBs along PAGBs, indicating that TMP, involving low deformation, could enhance the intergranular damage resistance.
分类: 物理学 >> 核物理学 分类: 核科学技术 >> 核聚变工程技术 提交时间: 2024-02-27
摘要: The helium bubbles induced by 14 MeV neutron irradiation can cause intergranular fractures in reduced activation ferritic martensitic (RAFM) steel, which is a candidate structural material for fusion reactors. In order to elucidate the susceptibility of different grain boundaries (GBs) to helium-induced embrittlement, the tensile fracture processes of 10 types of GBs with and without helium bubbles in body-centered cubic (bcc) iron at the relevant service temperature of 600 K were investigated via molecular dynamics methods. The results indicate that in the absence of helium bubbles, the GBs studied here can be classified into two distinct categories: brittle GBs and ductile GBs. The atomic scale analysis shows that the plastic deformation of ductile GB at high temperatures originates from complex plastic deformation mechanisms, including the Bain/Burgers path phase transition and deformation twinning, in which the Bain path phase transition is the most dominant plastic deformation mechanism. However, the presence of helium bubbles severely inhibits the plastic deformation channels of the GBs, resulting in a significant decrease in elongation at fractures. For bubble-decorated GBs, the ultimate tensile strength increases with the increase of the misorientation angle. Interestingly, the coherent twin boundary Ʃ3{112} was found to maintain relatively high fracture strength and maximum failure strain under the influence of helium bubbles.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: The physics potential of detecting $^8$B solar neutrinos is exploited at the Jiangmen Underground Neutrino Observatory (JUNO), in a model independent manner by using three distinct channels of the charged-current (CC), neutral-current (NC) and elastic scattering (ES) interactions. Due to the largest-ever mass of $^{13}$C nuclei in the liquid-scintillator detectors and the potential low background level, $^8$B solar neutrinos would be observable in the CC and NC interactions on $^{13}$C for the first time. By virtue of optimized event selections and muon veto strategies, backgrounds from the accidental coincidence, muon-induced isotopes, and external backgrounds can be greatly suppressed. Excellent signal-to-background ratios can be achieved in the CC, NC and ES channels to guarantee the $^8$B solar neutrino observation. From the sensitivity studies performed in this work, we show that one can reach the precision levels of 5%, 8% and 20% for the $^8$B neutrino flux, $\sin^2\theta_{12}$, and $\Delta m^2_{21}$, respectively, using ten years of JUNO data. It would be unique and helpful to probe the details of both solar physics and neutrino physics. In addition, when combined with SNO, the world-best precision of 3% is expected for the $^8$B neutrino flux measurement.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: This paper proposes a novel calibration-free wavelength modulated spectroscopy (WMS) spectral fitting technique based on the firefly algorithm. The technique by simulating the information interaction behavior between fireflies to achieve the retrieval of gas concentration and laser parameters. Contrasted with the spectral fitting technique based on the classical Levenberg-Marquardt (LM) algorithm, the retrieval of gas concentrations by this technique is weakly dependent on the pre-characterization of the laser parameters. We select the P(13) absorption line of C2H2 at 1532.82 nm as the target spectra and compare the performance of two optimization method (LM and firefly) on gas concentration and laser parameters retrieval by simulation. The simulation results show that the spectral fitting technique based on the firefly algorithm performs better in terms of convergence speed and fitting accuracy, especially in the multi-parameter model without exact characterization.
分类: 物理学 >> 核物理学 提交时间: 2016-09-05
摘要: The upgrade of the current BESIII Endcap TOF (ETOF) is carried out with the Multi-gap Resistive Plate Chamber (MRPC) technology. The installation of the new ETOF has been finished in October 2015. The first results of the MRPCs commissioning at BESIII are reported in this paper.
分类: 物理学 >> 核物理学 提交时间: 2016-09-01
摘要: The Beijing Spectrometer III (BESIII) endcap Time-Of-Filght (ETOF) was proposed to upgrade with Multigap Resistive Plate Chamber (MRPC) technology to substitute the current ETOF of scintillator+PMT for extending time resolutin better than 80 ps and enhance the particle identification capability to satisfy the higher precision requirement of physics. The ETOF system including MRPC modules, front end electronics (FEE), CLOCK module, fast control boards and time to digital modules (TDIG), has been designed, constructed and done some experimental tests seperately. Aiming at examining the quality of entire ETOF system and training the operation of all participated parts, a cosmic ray test system was built at the laboratory and underwent about three months to guarantee performance. In this paper the results will be presented indicating that the entire ETOF system works well and satisfies the requirements of the upgrade.