Study on Transient Gap Resonance with Consideration of the Motion of Floating Body

In this paper, the transient fluid resonance phenomenon inside a narrow gap between two adjacent boxes excited by the incident focused waves with various spectral peak periods and focused wave amplitudes is simulated by utilizing the open-sourced computational fluid dynamics software, Open FOAM. The weather-side box is allowed to heave freely under the action of waves, and the lee-side box keeps fixed. This paper mainly focuses on how both the spectral peak period and the focused wave amplitude affect the free-surface amplification inside the gap, the motion of the weather-side box, and the wave loads(including the vertical and the horizontal wave forces) acting on both boxes.For comparison, another two-box system with both boxes fixed is also considered as a control group. It is found that the motion of the weather-side box significantly changes the characteristics of the transient gap resonance, and it would cause that the fluid resonant period becomes 1.4-1.6 times that of the two-box system with both boxes fixed.All the concerned physical quantities(i.e., the free-surface amplification in the gap, the motion of the weather-side box, the wave loads) are found to closely depend on both the spectral peak period and the focused wave amplitude.

Magnetic resonance imaging in patients with transient ischemic attack

Transient ischemic attack （TIA） is a temporary event, which portends a higher risk of a disabling stroke following the TIA. However, the evaluation and management of TIA vary worldwide and is debated and controversial. With the development of brain imaging, particularly diffusion weighted imaging-magnetic resonance imaging （DWI-MRI）, the diagnosis of TIA changed from time-based definition to a tissue-based one. DWI-MRI be-came a mandatory tool in the TIA workup. The DWI-MRI provides not only the evidence to distinguish between TIA and acute ischemic stroke, fur-thermore it predicts TIA patients who are at higher risk of disabling stroke, which can be prevented by an immediate evaluation and treatment of TLA.

Realization of nonreciprocal acoustic energy transfer using an asymmetric strong nonlinear vibroacoustic system

In this paper,an asymmetric vibroacoustic system that can passively realize nonreciprocal transmission of acoustic energy is reported.This experimental system consists of a waveguide,a strongly nonlinear membrane,and three acoustic cavities with different sizes.The theoretical modeling of the system is verified by experiments,and parametric analysis is also carried out.These intensive studies reveal the nonreciprocal transmission of acoustic energy in this prototype system.Under forward excitation,internal resonance between the two nonlinear normal modes of the vibroacoustic system occurs,and acoustic energy is irreversibly transferred from the waveguide to the nonlinear membrane.However,under backward excitation,there is no internal resonance in the system.Energy spectra and wavelet analysis are used to highlight the mechanism of nonreciprocal transfer of acoustic energy.Consequently,nearly unidirectional(preferential)transmission of acoustic energy transfer is shown by this system.The nonreciprocal acoustic energy transfer method illustrated in this paper provides a new way to design the odd acoustic element.