摘要:

The method of determination of the optimum frequencies for active sonar without knowledge of the absolute values of the sonar‐set parameters, but only of their frequency dependence, appears to have been originated by J. W. Horton in about 1945 and is to be found in his recent text. This theory has been simplified and extended to include search rate,time‐processing gain, and the ratio of echo‐to‐noise‐plus‐reverberation. The inclusion of these new factors only slightly modifies the results obtained by maximizing echo‐to‐noise ratio alone because of the dominant effect of the frequency dependent exponential attenuation term in the transmission loss. Because of the octave or greater width of the maxima and the lack of precision in the knowledge of the frequency dependencies, the optimum frequencies should be looked on only as broad regions. For longer‐range and hence lower‐frequency active sonata operating at their optimum frequencies the energy of the pulse required per unit area or volume searched increases rapidly with the design range to a high exponent for the cases considered. This corollary is probably of little practical significance since the cost of operating power is usually small compared to other costs.

ISSN:0001-4966    

DOI:10.1121/1.1908958

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Preliminary research confirms that microbubbles become stabilized in a body of water and persist for long periods of time in contradiction of classical theory. The evidence was obtained by generating bubbles at the bottom of a water tank and then measuring the decay of ultrasonic attenuation as bubbles of various sizes rose to the surface. Comparison of experimental and classical decay curves disclosed persistence that appeared to be a function of the solid particle content of the water and indicated that bubbles may stabilize at sizes as large as 30 μ radius in water of high particulate content. In waters of low particulate content the decay of attenuation lasted over 100 hr.Substantial persistent abnormal attenuation was detected in all fresh tap water measured, amounting to a minimum 44% over that of distilled water (at 5.125 Mc) and is believed to be caused by stabilized bubble nuclei somewhat less than 0.8 μ in size. An interesting discovery was that attenuation rose in an uncovered test basin but fell in a covered basin, indicating that microbubbles may enter water on dust particles.A hypothesis presented to explain the persistence effect suggests that solid particles collect on the bubble surface, forming a compressed wall capable of supporting the excess pressure necessary to halt gas diffusion. Other hypotheses explore the mechanism by which dust particles may carry air globules below the water surface, and the dynamics of microbubble populations.

ISSN:0001-4966    

DOI:10.1121/1.1908960

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

The fact that Weber's law appears to apply in the same way both to intensity discrimination for pure tones and to intensity discrimination for white noise poses a theoretical paradox: in the case of pure tones, the human observer becomes less efficient as the intensity of the tone is increased, while in the case of white noise he exhibits a constant efficiency independent of intensity.An inventory of the various possible noise sources which may exist is made, and the way in which these may be expected to effect the detectability of a signal leads to the equation(d′)2=η2E&Dgr;NG+NE+kV02, where η is the individual observer's efficiency,NGis the noise introduced by the experimenter,NEis the uncontrolled noise present in the experimental situation, andkis a constant indicating that small amplitude variation in the oscillator constitutes a noise source proportional to the power of the lower of two signals to be discriminated.Data for three observers over four noise levels is described by this equation sufficiently well to suggest that the hypothesis that Weber's law is merely a reflection of the oscillator noise(kV02)is plausible.

ISSN:0001-4966    

DOI:10.1121/1.1908962

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

The exact Lagrangian formulation for one dimensional, rectilinear motion of a viscous, thermally conducting fluid is derived from the corresponding Eulerian formulation. Applicable results are compared with the Lagrangian equations given by Fay (1931) and Lindsay (1960).

ISSN:0001-4966    

DOI:10.1121/1.1908966

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1908968

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

A review of recent developments in the synthesis of stepped quarter‐wave transformers and half‐wave filters is given. A recent paper by Holte and Lambert is discussed.

ISSN:0001-4966    

DOI:10.1121/1.1908970

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

By use of a ray acoustical model of the ocean with linear sound speed gradients, the intensity is calculated when a ray is horizontal at a layer interface.

ISSN:0001-4966    

DOI:10.1121/1.1908972

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP