RESUMO
The Janus-Helmholtz (JH) transducer is a low-frequency, high-power, broadband underwater transducer type. Numerous studies have shown the effectiveness of the finite element method (FEM) in designing JH transducers and predicting their electroacoustic performance. However, a precise theoretical model for JH transducers has not yet been proposed, and the modal identification problem of JH transducers remains unsolved. In this paper, a distributed parameter model (DPM) of the JH transducer is proposed, which consists of the DPM of a Janus transducer and the DPM of a cylindrical liquid cavity under elastic wall conditions. By comparing the DPM with FEM, it is confirmed that the DPM can accurately calculate the resonant frequencies, admittance, amplitude, and phase of vibration velocity of the JH transducer. Additionally, a physical analogy is introduced to reveal the relationships between the transducer's resonances. Two JH transducers with different liquid cavities are fabricated and tested, and the results from the DPM, FEM, and experiments exhibit good agreement. The DPM can not only provide valuable theoretical support but also significantly reduce much time in designing JH transducers. Furthermore, it may inspire further advancements in adjusting the resonant frequencies or expanding the working bandwidth of JH transducers.
RESUMO
BACKGROUND: Vertebral artery origin stenting (VAOS) is the mainstream method for the treatment of vertebral artery stenosis (VAS). However, there are few studies on the risk factors analysis for residual stenosis after VAOS. PURPOSE: This study aimed to apply color Doppler ultrasound (CDU) to evaluate and analyze the risk factors of residual stenosis after VAOS. METHODS: About 178 patients with VAOS were included from 2017 to 2019 in Liuzhou worker's hospital and divided into the residual stenosis group (n = 38) and the no-residual stenosis group (n = 140). The clinical data and hemodynamics alteration before and after VAOS were collected. The univariate and multivariate logistic regression analysis was used to analyze the risk factors of residual stenosis. RESULTS: Compared with the no-residual stenosis group, the proportion of hypertension, the bending of the initial segment, and the residual stenosis length > 10 mm in the residual stenosis group were significantly higher, while the original internal diameter was significantly smaller (P < 0.05). The multivariate logistic regression analysis showed that the bending of initial segment (OR = 2.41, 95% CI: 1.32-5.45, P = 0.033), the original internal diameter (OR = 2.29, 95% CI: 1.13-5.66, P = 0.001), and the residual stenosis length > 10 mm were the risk factors of residual stenosis (OR = 2.78, 95% CI: 1.82-5.85, P = 0.044). CONCLUSION: The bending of initial segment, the original internal diameter, and the residual stenosis length > 10 mm were the risk factors of residual stenosis after VAOS.
