In this study, the influence of distance between the focusing lens and target surface on the plasma temperature of copper induced by a Nd:YAG laser was investigated in the atmosphere. The plasma temperature was calculated by using the Cu (I) lines (510.55 nm, 515.32 nm, and 521.82 nm). The Cu (I) lines were recorded under different lens-to-sample distances and laser pulse energies (15.8 mJ, 27.0 mJ, 43.4 mJ, 59.2 mJ, and 76.8 mJ). The results indicated that the plasma temperature depended strongly on the distance between the focusing lens and target surface. With the increase in the distance, the plasma temperature firstly rose, and then dropped. This could be attributed to the interaction between the tailing of the nanosecond laser pulse and the front portion of the plasma plume, the plasma shielding effect, and the expanding of the plasma. In addition, there was an interesting phenomenon that the plasma temperature and the emission intensity were not completely consistent with the change of the lens-to-sample distance. It is hoped that our research will provide a deeper insight into the underlying physical processes.

Influence of distance between focusing lens and target surface on laser-induced Cu plasma temperature Physics of Plasmas 25, 033302 (2018); https://doi

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The effect of spatial confinement on femtosecond laser-induced Cu plasmas was investigated by time-resolved spectroscopy. The cylindrical cavities with various diameters (2 and 3 mm) and various heights (2, 3, and 4 mm) were placed on the sample surface. An obvious enhancement in the emission intensity of Cu atomic lines was observed when a cylindrical cavity was used to confine the femtosecond laser-induced Cu plasmas. The results showed that enhancement ratios in femtosecond laser-induced breakdown spectroscopy with spatial confinement varied with cavity diameters and atomic emission lines selected. The spatial confinement effect was not significantly influenced by the cavity height because the height of plasma plume is lower than the cavity height. The maximum enhancement ratio for the emission intensities of the Cu atomic lines was measured to be around 3 at a time delay of 3.5 μs when the cavity diameter is 2 mm. The spectral enhancement is attributed to the compression of the plasma by the reflected shock wave.

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The Coronavirus Disease-19 (COVID-19) pandemic has dramatically affected residents' life. Whether the COVID-19 pandemic has significantly influenced the residents' health-promoting lifestyle, and life satisfaction is an urgent problem to be studied. Based on Health Belief Model (HBM), this paper explored and compared the responses of residents' health-promoting lifestyle and life satisfaction on the influence of the COVID-19 pandemic. Data were collected from a sample of 2,054 residents in Wuhan by questionnaire survey. The results show that the total score of health-promoting lifestyle after the COVID-19 pandemic has increased significantly compared with that before the COVID-19 pandemic, and the scores of all dimensions of health-promoting lifestyle have improved. Among them, the scores of exercises, self-actualization, and stress management are significantly higher than those before the COVID-19 pandemic. However, the score of residents' life satisfaction has shown a downward trend. There were also significant differences in life satisfaction on the demographic variables, such as gender, age, education level, marital status, and family average income. The findings are of great significance in promoting residents' health-promoting lifestyles and life satisfaction in the context of the extraordinary pandemic.

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