摘要:

A derivation is presented in which the normal modes of vibration are found for a continuous beam on simple supports. No conditions of symmetry are imposed and each span may have an arbitrary flexural rigidity that is constant throughout each particular span.

ISSN:0001-4966    

DOI:10.1121/1.1919297

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

The fluctuation of acoustic signals scattered from the ocean bottom displays a beat or interference characteristic when the source and/or receivers are in motion. Beat rates obtained statistically from observed data are shown to vary with velocity of source and receiver, as well as with transmitted frequency and acoustic geometry. Data obtained with a conical beam at a frequency of 19.5 kc/sec are compared with a simple physical model. Experimental results of a method for controlling the heat rate by linear frequency modulation of the transmitted signal are illustrated. Implications of the observations relative to reflection and scattering theory are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1919298

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

Shallow‐water ambient‐sea‐noise measurements in the frequency range 20 3000 cps have been made in the Gulf of St. Lawrence off the north coast of Prince Edward Island, with and without ice cover. The presence of ice is found to make a large difference both to the level and to the spectral distribution of the ambient noise. Result,are presented that illustrate both the effect of ice cover on the ambient noise and the transition from the “open‐water” to the “ice‐cover” condition.

ISSN:0001-4966    

DOI:10.1121/1.1919299

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

The sound‐channel region in the ocean is traditionally assumed to be stable and uniform over large areas, although indications of rapid and appreciable variations have been observed. To improve understanding of the true situation, a study of the fine structure and short‐term temporal and spatial variations in this region has been undertaken. The instrumentation and method developed for this purpose are described briefly. An underwater package containing two independent velocimeters, an FM pressure gauge, and auxiliary circuitry is repeatedly lowered and raised on a single‐conductor armored cable through the channel region. Sensor information is telemetered to the ship and recorded. Results from three stations south of Bermuda in the Fall of 1963 are described and analyzed. A surprising amount of activity is found, proving that the sound‐channel region, at the base of the main thermocline, is subject to much larger rapid changes than generally recognized. Considerable fine structure, evidence of internal waves, layers, and cells of “strange” waters have been observed. Sound‐velocity changes of several meters per second in a few hours, at the same depth, are common. From August to October, the average sound velocity on the axis has decreased from 1494.5 to 1491 m/sec, the axis depth from 1300 to 1150 m.

ISSN:0001-4966    

DOI:10.1121/1.1919300

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

Absolute intensive thresholds are presented from 26 men yielding Békésy audiograms at 20 frequencies. Results validate the practice of graphic interpolation between thresholds in octave steps to predict mean thresholds at half octave points. Thresholds are almost indistinguishable from those by conventional audiometry in a very similar population. Data are interpreted to confirm in general the practicability of using the proposed 1964 ISO reference threshold level as the norm for young otoscopically negative adults.

ISSN:0001-4966    

DOI:10.1121/1.1919301

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

Two transientfree switches are described. One is manually controlled and has fixed rise and decay times of 125 and 135 msec, respectively. The second switch can be triggered either repetitively or manually and the rise times can be adjusted for 0.25, 0.5, or 1.0 msec.

ISSN:0001-4966    

DOI:10.1121/1.1919302

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

Single‐unit activity was recorded from the eighth nerve of the green frog. All units are frequency‐selective. Units most sensitive to tone bursts of frequencies below 450 cps show little or no spontaneous activity; their responses to tone bursts can be inhibited by tones of frequency above 500 cps. Many of these low‐frequency units are sensitive to vibration and their responses to vibration can also be inhibited. Units with most sensitive frequencies above 650 cps are spontaneous and cannot be inhibited. These high‐ and low‐frequency units probably originate from different sense organs within the otic capsule, and evidence supporting this supposition is presented. Ten units displaying very different response patterns are also discussed. Results of this study are compared with those of Frishkopf and Goldstein for the bullfrog.

ISSN:0001-4966    

DOI:10.1121/1.1919303

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

Use of short pure‐tone bursts to test perception of tone rather than click in cases of disturbed blood Supply to the brain stem in humans has shown that the threshold of tonal processing provides an approach to measurement of neural processes in pitch perception.

ISSN:0001-4966    

DOI:10.1121/1.1919305

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1919306

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

A reanalysis of pure‐tone thresholds and speech‐discrimination (PB) scores for groups of ears with perceptive loss, mixed loss, or normal hearing showed that there is no clear superiority for the average of one set of three frequency (1000, 2000, and 3000 cps) over another set of three frequencies (500, 1000, and 2000 cps) for predicting PB score.

ISSN:0001-4966    

DOI:10.1121/1.1919307

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP