Micro-impulse and plasma plume produced by irradiating aluminum target with nanosecond laser pulses in double-pulse scheme

The micro-impulse generated by ablating an aluminum target in double-pulse laser bursts with different interpulse delays was investigated using a torsion pendulum.The plasma plume was simultaneously visualized using high-speed photography to analyze the coupling mechanism of the ablation impulse.The experiment was carried out using a pulsed laser with a pulse width of 8 ns and a wavelength of 1064 nm.The experimental results show that an impulse with an interpulse delay of 60 ns is roughly 60%higher than that with no delay between the two pulses,when the energy of both laser pulses is 50 m J.Therefore,double-pulse schemes could enhance the ablation impulse under certain conditions.This is because the ablation of the first laser pulse changes the optical properties of the aluminum target surface,increasing the absorptivity.However,the ablation impulse is reduced with a time delay of 20 ns when the energy of both laser pulses is100 mJ or 150 mJ.It can be concluded that the plasma produced by ablating the aluminum with the first pulse shields the second laser pulse.To summarize,the experimental results show that different delay times in a double-pulse scheme have a significant effect on the ablation impulse.The study provides a reference for the optimization of the parameters when laser ablation propulsion with a double-pulse scheme is applied in the fields of space debris removal,laser ablation thrusters,and so on.

Test and Evaluation of ECMWF Model on Precipitation Forecast in Shaoyang Area

Using actual precipitation in Shaoyang of 2018-2020,precipitation forecast of ECMWF model was tested.The results showed that winter accuracy rate was the highest,followed by autumn,and summer accuracy rate was the lowest.24-h TS scoring results showed that the shorter the cumulative time,the lower the TS.Forecasters had a strong ability to predict summer rainstorms.

Photothermal‑Triggered Structural Change of Nanofiber Scaffold Integrating with Graded Mineralization to Promote Tendon–Bone Healing

Scaffolds functionalized with graded changes in both fiber alignment and mineral content are more appealing for tendon-bone healing.This study reports the healing of rotator cuff injury using a heterogeneous nanofiber scaffold,which is associated with a structural gradating from aligned to random and an increasing gradient of mineral content in the same orientation.The photothermal-triggered structural change of a nanofiber scaffold followed by graded mineralization is key to constructing such scaffolds.This type of scaffold was found to be biocompatible and provide beneficial contact guidance in the manipulation of tendon-derived stem cell morphologies in vitro.Specifically,tenogenic and osteogenic differentiation of tendon-derived stem cells were simultaneously achieved using the fabricated scaffold.In vivo investigation also showed the improved healing of rabbit rotator cuff injuries based on immunohistochemical analysis and biomechanical investigation that indicates the promising potential of a dual-gradient nanofiber scaffold in clinical tendon-bone healing.