The effects of the uneven bottom on horizontal longitudinal correlations of acoustic field in deep water

The spatial coherence of sound field in the reflection area of deep-water bottom is studied by analyzing the data of an acoustic propagation experiment conducted in the South China Sea. Some different oscillation patterns of the measured horizontal longitudinal correla- tions of acoustic field are observed for two different tracks in the flat bottom and the uneven bottom environments when the source distance ranges from 29 km to 35 km. Numerical analysis based on the ray theory is carried on to explain the causes of the differences. The experimental and mlmerical results show that the travel time differences between the one-bottom-reflection （1BR） rays, which make a major contribution to the sound field of the 1BR area in flat bottom environment, decrease gradually with increasing horizontal distance. Then the phase of the interference cyclically changes within 27r, leading to the correlations＇ periodical oscillation in deep water with flat bottom. In the uneven bottom environment, however, due to the reflection- blockage effects of the sea hill on the 1BR sound beams, the sound transmission losses （TLs） in- crease significantly in the reflection area of the sea hill. What＇s more, the horizontal-longitudinal correlations decreasing slightly in general don＇t show obvious cyclical oscillation any longer in the corresponding reflection area because of the complex interference of the relatively more eigenrays. This work is of significance to analyze the detection performance of the sonar array in deep water with the complicated bathymetry environment.

Evaluation of Myocardial Strain and Aortic Elasticity in Patients with Bicuspid Aortic Valve

This study evaluated the myocardial strain and aortic elasticity in patients with bicuspid aortic valve（BAV） and then investigated the relation between them. Thirty-nine patients（30 males; mean age 44±19 years; range 6 to 75 years） with BAV were recruited as BAV group, and 29 age- and sex-matched healthy controls（21 males; mean age 42±11 years; range 20 to 71 years） served as control group. Aortic strain, distensibility and stiffness index were derived using M-mode echocardiography. Left ventricular global myocardial strain was acquired with speckle-tracking echocardiography. Correlation between aortic elasticity and myocardial strain was also analyzed. The results showed that aortic stiffness was higher（17.5±14.0 vs. 5.3±2.7, P〈0.001）, and aortic strain（4.9±4.7 vs. 11.0±4.1, P〈0.001） and distensibility（1.8±2.1 vs. 3.7±1.6, P〈0.001） were lower significantly in BAV group than in control group. Global circumferential strain（–19.1±4.2 vs. –22.5±3.7, P〈0.001）, radial stain（29.8±14.9 vs. 38.0±8.8, P〈0.001） and longitudinal stain（–18.4±3.4 vs. –20.8±3.5, P〈0.001） were significantly lower in BAV group than in control group. There was weak association between aortic elasticity and myocardial strain. These findings indicated BAV patients manifest reduced myocardial strain which had weak relationship with aortic elastic lesion.

A review of research progress in air-to-water sound transmission

International and domestic research progress in theory and experiment and applications of the air-to-water sound transmission are presented in this paper. Four classical numerical methods of calculating the underwater sound field gener- ated by an airborne source, i.e., the ray theory, the wave solution, the normal-mode theory and the wavenumber integration approach, are introduced. Effects of two special conditions, i.e., the moving airborne source or medium and the rough air-water interface, on the air-to-water sound transmission are reviewed. In experimental studies, the depth and range distributions of the underwater sound field created by different kinds of airborne sources in near-field and far-field, the longitudinal horizontal correlation of underwater sound field and application methods for inverse problems are reviewed.