Effects of annular acoustic black holes on sound radiated by cylindrical shells

While most acoustic black hole (ABH) designs are intended to reduce vibrations in beams and plates, annular ABHs have been recently proposed for cylindrical shells. The key to achieve the ABH effect in a structure consists in embedding an indentation on it such that it slows down incident waves and concentrates their energy at the center of the ABH. There, it can be typically dissipated by means of a viscoelastic layer. Many studies exist on the vibration of structures with ABH indentations but only a few address the topic of sound radiation. In this work, we evaluate the impact that an annular ABH has on the sound radiated by a baffled cylindrical shell. The vibration of the cylinder is computed using Gaussian basis functions in the Rayleigh-Ritz method. Once determined the surface velocity of the ABH cylinder, a Green's function approach is employed to obtain its surface acoustic pressure and then the sound power level, radiation efficiency and supersonic intensity. The dependency of the latter on the ranges determined by the ring and critical frequencies is analyzed for the case of a thick acoustic shell. Beyond the critical frequency, supersonic flexural waves entering the ABH become subsonic, substantially reducing the radiation efficiency and therefore, the emitted sound. Further reduction is achieved once passed the ring frequency.

Retrieval of Cloud Liquid Water Using Microwave Signals from LEO Satellites: A Feasibility Study through Simulations

A novel approach, using low Earth orbit (LEO) satellite microwave communication links for cloud liquid water measurements, is proposed in this paper. The feasibility of this approach is studied through simulations of the retrieval system including a LEO satellite communicating with a group of ground receivers equipped with signal-to-noise ratio (SNR) estimators, a synthetic cloud attenuation field and a tomographic retrieval algorithm. Rectangular and Gaussian basis functions are considered to define the targeted field. Simulation results suggest that the proposed least-squares based retrieval algorithm produces satisfactory outcomes for both types of basis functions. The root-mean-square error of the retrieved field is around 0.2 dB/km, with the range of the reference field as 0 to 2.35 dB/km. It is also confirmed that the partial retrieval of the cloud field is achievable when a limited number of receivers with restricted locations are available. The retrieval outcomes exhibit properties of high resolution and low error, indicating that the proposed approach has great potential for cloud observations.

Kaonic deuterium from realistic antikaon-nucleon interaction

We present precise three-body calculations for the spectrum of kaonic deuterium with a realistic antikaon-nucleon interaction. Thanks to the precise measurement of kaonic hydrogen, it is now possible to construct realistic $\bar KN$ interactions which reproduce the whole set of experimental data in the threshold region. Employing such realistic interactions, the energy of the three-body system of kaonic deuterium is determined with the accuracy of eV, by expanding its wave function with a large number of correlated Gaussian basis functions. The level shift and width of the 1S state are found to be 670 eV and 1016 eV, respectively. The improved Deser formulas work reasonably well to estimate the shift and width of kaonic hydrogen, but their application to kaonic deuterium does not give an accurate estimation. It is shown that the result is sensitive to the I = 1 component of the $\bar KN$ interaction, which will be further constrained in future experiments.