[en] Femtosecond pulse laser ablation of aluminum under different ambient air pressures between 1 atm and 4 x 10^-4 Pa is investigated using a femtosecond time-resolved shadowgraphic method. It is observed that as the ambient air pressure decreases, the contact front becomes more and more distinct for a certain pressure range, demonstrating that the confinement effect of the ambient air to the ablated target material can play a critically important role in the laser ablation process. It is also found that the concentric and semicircular stripe pattern, which results from the diffraction of the probe beam by the expanding plume of a specific material state and is typically observed in the shadowgraphs for 1-2 ns delay time, gradually blurs and disappears while the ambient air pressure decreases from 1 atm to 7000 Pa. If a prepulse or a relatively large pulse pedestal exists before the main pulse, however, the stripe pattern can still be observed even though the ambient air pressure is 5 x 10^-4 Pa. It is thus inferred that what contributes to the formation of the unique stripe pattern is a mixture of the ejected target material and ionized background gas induced by the femtosecond laser ablation.

[en] Using multiple scavenger effects to investigate the radiolysis of cyclohexane has been reported. It was found that in the radiolysis of cyclohexane and 4-methyl-4-phenyl-2-pentanone, besides the excitation energy transfer, there is another important process happened, i.e., the capture of thermal hydrogen atoms. The rate constant of such process is obtained to be 2.5 x 10⁹ Lmol^-1s^-1, and the yield of the thermal hydrogen atoms 1.5 is also obtained

[en] Highlights: • Single 50 fs laser pulse ablation of an aluminium target in vacuum is investigated in our experiments. • Nanoparticles with large radii of several hundred nanometers are observed. • The nanoparticles are most likely from the mechanical tensile stress relaxation. - Abstract: Single femtosecond laser pulses are employed to ablate an aluminium target in vacuum, and the particle size distribution of the ablated material deposited on a mica substrate is examined with atomic force microscopy (AFM). The recorded AFM images show that these particles have a mean radius of several tens of nanometres. It is also determined that the mean radius of these deposited nanoparticles increases when the laser fluence at the aluminium target increases from 0.44 J/cm² to 0.63 J/cm². The mechanism of the laser-induced nanoparticle generation is thought to be photomechanical tensile stress relaxation. Raman spectroscopy measurements confirm that the nanoparticles thus produced have the same structure as the bulk aluminium

[en] Multiple scavenger effects have been used to investigate the radiolysis of cyclohexane. Using the excited singlet probes 4-methyl-4-phenyl-2-pentanome (MPP) and tributyl phosphate (TBP), we obtained the yields of the excited singlet state of benzene (1.4 ± 0.2), cyclohexane (1.5 ± 0.2), TBP (1.4 ± 0.3), the yield of the thermal hydrogen atoms of cyclohexane (1.5), and the yield of the germinate ions of cyclohexane (3.8). The multiple scavenger effects of MPP and TBP were successfully used in the research of hydrogen atom transfer process in the radiolysis of cyclohexane. (author)

[en] A special probe of excited singlet states was established. The Norrish type II elimination reaction of 4-methyl-4-phenyl-2-pentanone (MPP) induced by γ-rays was reinvestigated. By measuring the G value of the sensitization radiolytic product α-methylstyrene (α-MS), we obtained the G value of excited singlet states. It was found that the G value of benzene excited singlets is 1.4 ± 0.2, the rate constant of excitation energy transfer from benzene excited singlet to MPP is (5.2 ± 0.5) x 10⁹ dm³ mol^-1 s^-1; the G value of excited tributylphosphate singlets is 1.4 ± 0.3, the lifetime of its excited singlets is (1.3 ± 0.1) x 10^-7 s; the G value of excited cyclohexane singlets is 1.5 ± 0.2, the rate constant of excitation energy transfer from cyclohexane excited singlets to MPP is (4.1 ± 0.4) x 10¹⁰ dm³ mol^-1 s^-1. It was found that MPP has multiple effects in quenching the active species formed in the radiolysis of benzene and tributylphosphate, both excitation energy transfer and reaction with subexcitation electrons have occurred. A yield of subexcitation electrons of benzene 4.0, that of tributylphosphate 5.0, was obtained. The kinetics of both processes were also discussed. (author)

[en] Published in summary form only

[en] A new practical model of image acquisition circuit is given. It can be applied to data acquisition system of γ camera from nuclear medicine directly. Its idea also can be applied to some image acquisition system of nuclear event

[en] Magnetic domain structure of FeCoBSi antidot array thin films of varying thickness were characterized using surface magneto-optic Kerr effect. Vibrating sample magnetometry and microstrip transmission line measurements helped to associate the microwave magnetic analysis of the antidot arrays with hysteresis studies. The domain structure evolution from quasi-continuous domains to strip domains induced by the competing exchange and dipolar interaction resulted in the change of ferromagnetic resonance from multi-band to single-band. Hence, the mechanisms of multi-resonance are proposed to be related to domain wall motion, natural resonance and spin wave modes. This phenomenon can be used to control the magnetization dynamics in spin wave devices. - Highlights: • A multiresonance mechanism for ferromagnetic antidot array is proposed. • The mechanism relies on the domain structure evolution of antidote arrays. • Domain structure of antidot arrays changes from quasi-continuous patterns to strip domains. • Resonance of domain wall motion is discriminated from the natural resonance and spin wave modes

[en] Highlights: • A two-phase boundary layer (TPBL) model is evaluated adequately via a CFD code. • Predicted heat transfer properties are consistent with the COPAIN experimental data. • Thin liquid film with small thermal resistance is developed on heat transfer surface. • The TPBL model takes longer time to reach a quasi-steady state. • Predicted local field profiles are consistent with the TOSQAN results. - Abstract: Steam condensation in the presence of air is a vital heat transfer process in postulated loss of coolant accidents. To numerically evaluate local and global thermal hydraulic properties, several single-phase models have been developed in previous studies. However, potential mutual interactions between the liquid and gas phase (e.g. evaporation, radioactive material retention, etc.) impose requirements on two-phase models. Accordingly, the present work performed CFD evaluations on a two-phase boundary layer model (TPBL) which concerned the gas phase, liquid phase and their mutual interactions. Assessments were performed by comparing calculated results with the COPAIN and TOSQAN experimental data. The COPAIN cases show that predicted local and average heat fluxes are generally within 25% and 15% deviation, respectively. Detailed properties were obtained on the formation, distribution, and thermal resistance of liquid film as well as the model computational costs. In the TOSQAN cases, two steady states, including steam-air mixtures and steam-air-helium mixtures were considered. Via these cases, the applicability of the TPBL model in predicting local field profiles like velocity, temperature and concentration distribution was discussed. Results demonstrate that the calculated results overall agree well with the experimental ones. In general, the TPBL model is feasible in postulated accident analysis.

[en] Based on the new concept water-cooled packed bed reactor, the resistance characteristics of air-water flow upward through sphere-filled channel have been studied experimentally. The channels are packed with glass spheres of which the diameters are 2, 5 and 8 mm respectively. Experimental results show that the pressure drop increases with the increase of gas-liquid mass flow rate, and has a certain relationship with the flow patterns. The particle diameter and porosity have great influence on the pressure drop at the same flow condition. The published pressure drop correlations are grouped into two types (the separate flow model and the homogeneous model). The two types of correlations are compared and modified, combined with 234 group experimental data. It is found that: (1) the best agreement between measured and calculated values is obtained with the correlations based on the separate flow model, but the predictive ability is reduced with the increase of particle diameter. (2) the existing homogeneous model show the considerable discrepancies with this experiment values, however the modified homogeneous correlation is in good agreement with the experimental data. (authors)