摘要:

A method is proposed by which the incidence of motion sickness may be predicted from measurement of the motion exposure. The method is based on data from both field and laboratory studies involving large numbers of people and is applicable to marine and other environments where vertical oscillation occurs at frequencies below 0.5 Hz. The dependence of motion sickness on the frequency of oscillation requires the use of a weighting function between 0.1 and 0.5 Hz. The dependence of sickness on the duration of exposure is incorporated by the use of a cumulative measure of motion dose based on the product of root‐mean‐square (rms) acceleration magnitude and the square root of stimulus duration. The influence of population variables such as sex, age, and motion experience is discussed. The method enables separate predictions to be made of vomiting incidence and of feelings of illness. The prediction procedure, while not seeking to explain the underlying mechanisms of motion sickness occurrence, provides a generally applicable method which is simple to use and has an accuracy consistent with the experimental data on which it is based.

ISSN:0001-4966    

DOI:10.1121/1.395295

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The intensity coherence function (ICF) of the acoustic wavefunction from a point source is derived by the path‐integral technique for transmission through internal waves in the presence of a sound channel. Separations in time are emphasized, although separations in transverse horizontal position, vertical position, and acoustic frequency are discussed. Approximate intensity coherence times, lengths, and bandwidths due to internal‐wave fluctuations are derived. Analytic approximations suitable for computer coding are presented for the micropath focusing parameter γ, which controls the deviation of higher intensity moments from the Rayleigh‐distribution values.

ISSN:0001-4966    

DOI:10.1121/1.395296

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

In an acoustic‐oceanographic experiment (AFAR) performed near the Azores in 1975, frequencies from 400–4670 Hz were transmitted over a 35‐km wholly refracted path. In addition, a separate data set was gathered over a 3‐km path in 1973. Measurements of the intensity coherence function of time and frequency, intensity moments, and the probability distribution of intensity are presented and compared with predictions of fluctuations due to internal waves.

ISSN:0001-4966    

DOI:10.1121/1.395297

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Insitumeasurements of fish target strength are selected for use in echo integrator surveys at 38 kHz. The results are expressed through equations in which the mean target strength TS is regressed on the mean fish lengthlin centimeters. For physoclists, TS=20 log l−67.4, and for clupeoids, TS=20 log l−71.9. These equations are supported by independent measurements on tethered, caged, and freely aggregating fish and by theoretical computations based on the swimbladder form. Causes of data variability are attributed to differences in species, behavior, and, possibly, swimbladder state.

ISSN:0001-4966    

DOI:10.1121/1.395298

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Data from the Beaufort Sea are used to quantify some of the seasonal characteristics of under‐ice ambient noise. Noise at 10, 32, and 1000 Hz was studied and seasonal space and time scales were calculated. An interesting result is that summer 10‐Hz noise apparently can often be contaminated by cable strum. The summer period is also the only time during which 1000‐Hz noise is almost totally a product of ice motion. Within the central Beaufort Sea, lower frequency noise tends to havee‐folding space scales of the order of 1000 km. This is true for 1000‐Hz noise only during summer, with space scales for the rest of the year being ∼300 km. The time scale analysis also shows this trend. During summer, all frequencies havee‐folding time scales of the order of 10–30 h. During fall and winter, the time scales for lower frequencies increase (up to 72 h or longer), but the 1000‐Hz time scales drop to as low as 3 h.

ISSN:0001-4966    

DOI:10.1121/1.395299

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Three perturbative inverse methods for obtaining bottom geoacoustic parameters as a function of depth in shallow water are described. The required input data are the trapped mode eigenvalues for one or more frequencies, the group velocity dispersion curves for one or more modes, or the cw pressure field versus range. In each case, a Fredholm integral equation arises that can be solved using linear inverse theory, and for which resolution and variance estimates of the solution can be readily made. Attention is focused primarily on the modal eigenvalue inverse problem for which the theory for determining the compressional wave speed, compressional wave attenuation, and density is developed in detail. Properties of this technique are studied using synthetic data and include investigations of the dependence of the results on acoustic frequency, number of modes excited, and partialaprioriknowledge of the bottom. The method is demonstrated on experimental data obtained in Nantucket Sound at 140 and 220 Hz. Directions of future research on these techniques are indicated.

ISSN:0001-4966    

DOI:10.1121/1.395300

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The oscillations and sound emission of a bubble cloud containing a large number of bubbles in a liquid are studied. Averaged equations are used to describe the behavior of the mixture. Two analytical models are used to describe the behavior of the bubble contents. The oscillations of small amplitude are calculated analytically, those of not so small amplitude numerically. It is shown that the frequency spectrum is determined mainly by the total volume of gas in the cloud. The efficiency of sound emission is determined also by the magnitude of the individual bubbles. The frequency spectrum of the emitted sound has a peak at a frequency much lower than the eigenfrequency of the individual bubbles. At higher amplitudes of the oscillations, very high pressures occur at the center of the cloud that strongly limit the numerical calculations.

ISSN:0001-4966    

DOI:10.1121/1.395376

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

A towed array experiment was performed by NRL in 1982 in the vicinity of the ice edge in the Greenland Sea. The array was towed normal and parallel to and at ranges between 4–50 km from the ice edge; the received data were beamformed to study the horizontal directionality of the noise. The results indicated that a few localized ‘‘hot spots’’ (with dimensions<5 km) in the vicinity of the ice edge were the dominant noise sources. These sources persisted for nearly 1 day. The nominal separation between the hot spots was about 50 km. The ice edge noise spectrum measured at these ranges decreased 11–12 dB per octave with frequency between 100–500 Hz, as compared with the 6 dB per octave spectrum of ambient sea noise. Possible sources are hypothesized in the context of known eddy, wind, and wave effects in the vicinity of the ice edge.

ISSN:0001-4966    

DOI:10.1121/1.395377

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The acoustic radiation force was measured for a dual‐temperature resonant chamber. This rectangular chamber has its long dimension approximately 8.5 times the square cross‐sectional dimension, and the opposite ends are at widely different temperatures. Force profiles were obtained for two hot end temperatures of 520 °C and 760 °C, while the cool end remained at approximately room temperature. The lateral force was measured as a function of the long dimension of the chamber along the temperature gradient, and as a function of the drive voltage. Force magnitudes as high as 17 dyn for a sample 1.2 cm in diameter at 760 °C and at 162‐dB input level were measured. Qualitatively, the measured force profiles correspond well with the theoretical curves; the correlation of absolute magnitude, however, is yet to be determined.

ISSN:0001-4966    

DOI:10.1121/1.395378

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The method of matched asymptotic expansions is used to determine a low‐frequency approximation of the acoustic pressure in a waveguide system with a T joint. The low‐frequency approximation is compared with (a) experimental data of Lippert [Acustica4, 313–319 (1954)]; (b) new experimental data; and (c) the first approximation of the mode expansion proposed by Miles [J. Acoust. Soc. Am.17, 259–272 (1946)].

ISSN:0001-4966    

DOI:10.1121/1.395379

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP