Graphical abstract
A fiber-based optoacoustic emitter is developed, serving as the most miniaturized ultrasound point source so far, with sub-millimeter confinement. Controllable frequencies are achieved and further induce cell membrane sonoporation with frequency dependent efficiency. By solving the problem of compromise between sub-MHz frequency and sub-millimeter precision via breaking the diffraction limit, the FOE shows a great potential in region-specific cell modulation.
A type of non-contact mechanical face seal supported by a disc spring with high bending stiffness is proposed for actual working conditions and may be used in high-speed turbopumps with large axial loads and heavy random vibration. First, the separated speed of the seal is obtained, which shows that the initial contact mechanical seal can transform into a noncontact seal when the rotational speed is higher than the separated speed. Second, the steady-state model is proposed to describe the performance of the seal. The model includes the Reynolds equation, energy equation, lubricant temperatureviscosity relationship equation, and moment equilibrium equation, and the finite-difference method is used to solve the model. Third, with water as the sealed fluid, the effects of the geometric parameters and working parameters (e.g. spring stiffness, axial load, rotational speed) on the main performance parameters (film thickness, the maximum pressure, temperature, power loss, leakage) are obtained. The results show that with an increase in the stiffness of the spring, the film thickness and temperature increase change only slightly. With an increase in seal load, the film thickness decreases and the temperature increases. The film thickness increases and the temperature decreases with an increase in rotational speed. The results show that the proposed mechanical seal supported by such disc spring can be used in turbopump systems with higher speeds and smaller leakage requirements.
The third-harmonic (TH) emission characteristics from femtosecond laser filament, the center of which is screened by a thin metallic fiber, are experimentally investigated. The intensity of the TH emission has been enhanced for 1 order of magnitude by comparing with the undisturbed filament. The physical mechanism of the TH enhancement is analyzed to be the diffraction of the TH emission on the fiber and a redistribution of laser energy during the reconstruction of the two-colored filament. These two factors can release a part of the TH energy from the filament core into the background and keep more TH energy after the termination of filament.
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