摘要:

A relationship between capillary wave amplitude and the diameter of spherical particles ejected in an ultrasonic atomizer is developed. This relationship predicts a threshold amplitude for the generation of the aerosol and is based upon a bifurcation process to reduce surface energy. The most probable size of particles is found to be a diameter of 0.36λ, where λ is the wavelength of capillary waves for the system. This result is in excellent agreement with the previously reported empirical median particle diameter of 0.34λ.

ISSN:0001-4966    

DOI:10.1121/1.1910770

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

The thickness‐shear vibrations inAT‐cut quartz plates with partial electrodes including the effects of a pair of free edges are discussed in a qualitative manner. The frequencies and mode shapes as a function of plate and electrode dimensions are determined from an analysis similar to that of Mindlin and Lee. These results are compared with measured values obtained from rectangular quartz plates with rectangular electrodes. The ratio of capacitances of thickness‐shear vibrations are calculated from an expression given by Lewis. These calculations indicate that the ratio of electrode length to plate length is equally as important in the suppression of anharmonic thickness‐shear vibrations in finite quartz plates as is the ratio of electrode length to plate thickness (Bechmann's number).

ISSN:0001-4966    

DOI:10.1121/1.1910771

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

A study has been made of the influence on shock spectrum curves of the interaction between a superstructure and its nonrigid foundation. Such interaction causes the spectrum values of interest to lie in the valleys corresponding to the superstructure's fixed base natural frequencies, while the peak spectrum values occur at the combined system natural frequencies. Normal mode theory for lumped mass systems is reviewed briefly and the necessary equations are presented. These equations demonstrate how shock spectrum data are applicable for calculating deflections, stresses, etc., for structures subjected to transient excitations. The concept of design shock spectra is discussed, and an example shows how design spectrum data might be applied to a particular case.

ISSN:0001-4966    

DOI:10.1121/1.1910772

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

The modal density of a structural element is defined as the number of resonant modes within a unit frequency interval. In this paper, expressions are presented for the modal densities of some shallow sandwich shells, orthotropic plates, shells on an elastic foundation, pretwisted plates, and plates subject to in‐plane forces. The expressions are valid for elements of arbitrary shape and having any prescribed boundary conditions. It is shown that, except for the orthotropic plate, the modal density of all the elements is frequency‐dependent. As the frequency increases, the modal density of the shells approaches asymptotically that of the corresponding plate. For the sandwich elements, the modal density increases with increasing frequency, whereas the modal density of monocoque elements approaches a constant value.

ISSN:0001-4966    

DOI:10.1121/1.1910773

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

The transient process in acoustic fields generated by the time‐dependent motion of an arbitrary body submerged in an infinite, inviscid, and slightly compressible fluid is formulated by the source‐density method. The governing equations of the source density are solved exactly for the acoustic field generated by the arbitrarily time‐dependent motion of a rigid, circular baffled piston in a rigid infinite plane. In the general case, a numerical method of predicting the transient pressure field is developed according to the source‐density formulation. Three numerical examples are presented to demonstrate the versatility of the method. The numerical method proves to be useful for small values of time. However, for large values of time, the error introduced in the numerical solution becomes unacceptably large and the method is no longer valid.

ISSN:0001-4966    

DOI:10.1121/1.1910774

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Sonar systems currently in use and under development attempt to discover the presence of an underwater target by transmitting an acoustic pulse and detecting the echo with a correlation receiver. This receiver correlates its input with time and frequency translates of a stored reference waveform, usually the same as the transmitted waveform. Owing to the presence of random multipath, there is usually not a single echo, but a multiplicity of echoes with random attenuations, time delays, and frequency shifts. Under these conditions, the detection capability of the correlation receiver is shown to be dependent upon the transmitted and reference waveforms. Necessary and sufficient conditions for optimum waveforms under a maximum signal‐to‐noise ratio criterion with an energy constraint are derived. A technique for finding waveforms that satisfy only a necessary condition is demonstrated, but it is conjectured that it produces the optimum waveforms. Conjectured optimum waveforms are derived for selected examples, and their performance compared to that of some conventional waveforms.

ISSN:0001-4966    

DOI:10.1121/1.1910775

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Several acoustic and temporal variables responsible for the elicitation of the rat's startle reaction were examined by measuring the subject's overt movement under each of a variety of stimulus conditions. When startle was repeatedly evoked, the response decreased in amplitude, but adaptation was slow and was not complete after 675 stimulus presentations. The threshold for startle evocation increased with repeated stimulation, but partial recovery occurred during interpolated rest periods. Startle reactions were amplified when testing occurred in a background of steady noise, but the effect was independent of the frequency components of the background stimulation. Moreover, although a relatively weak signal could inhibit the reaction to a subsequently presented intense signal, the effect was independent of the frequency characteristics of either signal. Finally, it was found that relatively weak signals could either inhibit the startle reaction to a subsequently presented intense signal or reduce response latency, depending upon the temporal relationships between the two signals. It was concluded that weak signals can activate the neural mechanisms responsible for the startle reaction, and that the occurrence of acoustic startle along with its associated inhibitory and facilitory effects is dependent upon the sensation levels of the signals, but not upon their frequency characteristics.

ISSN:0001-4966    

DOI:10.1121/1.1910776

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Variation in sensitivity to an objective 2000‐Hz harmonic (f2) is produced at different intensities with a 1000‐Hz fundamental (f1) masker. This continuousf1pure tone is presented monaurally at 57, 61, 65, 67, 69, 71, or 74 dB SPL to each of seven normal ears. Simultaneously, the listeners trace Békésy‐type thresholds for the interruptedf2in the same ear. This objectivef2is then phase shifted, in 60° steps, through 360°. The threshold shift (TS) obtained has been described previously by the general equation,TS = A1+A2×sin (X+Φ). The present purpose is to confirm this observation by examination of a range off1intensities and to analyze separately any systematic changes in the three dependent variables;A1,A2, and Φ. Explanations of the effect off1intensity upon these parameters are derived from a model that makes three major assumptions: (a) The ear generates an aural harmonic (AH); (b) the AH sums vectorially with the objectivef2; and (c) the listener maintains a threshold response. The mean TS results fit the above equation at allf1intensities sampled here. Detailed analysis of the three dependent parameters reveals: (1) Linear increases inA1(slope 2.0–2.5 dB) forf1intensities above 60 dB; (2) complex changes inA2with relatively large individual differences; and (3) independence of Φ from increases inf1intensity. The simple model is useful in explaining the mechanisms underlying these parameters in the range off1intensities from about 45–50 dB to 74+dB SPL.

ISSN:0001-4966    

DOI:10.1121/1.1910777

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

An investigation is undertaken of the ability to hear a signal sound in the presence of noise, when the signal and the interfering sound each have a directional characteristic and are separated from each other more than a certain degree, compared with the case when both are not separated. We attempt to determine through what process in our auditory system such a phenomenon occurs. We think that, when there are many sounds coming from many directions, directional information is extracted from the neural signals from both ears in our auditory system, each sound is localized in each place or direction, and a certain particular sound is selected and listened to. There is considerable difference, in the subject's ability to hear the sound, between the case in which a subject concentrates his attention on it, and the case in which he does not. For this interpretation, “attention” is introduced. It is clarified that the function that maintains the attention leads to the selective hearing of a signal relative to its direction and timbre.

ISSN:0001-4966    

DOI:10.1121/1.1910778

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

The ability of subjects to detect sinusoidal signals in a continuous background of white Gaussian noise was investigated for several different interaural relations of the signal and of the noise stimuli. The functions, referred to as receiver operating characteristics (ROC's), relating the proportion of correct detections of the signal to the proportion of false alarms were determined in each case. A rating procedure was employed to determine the ROC's. The area under the ROC was found to be a good estimate of the percent correct obtained with a two‐interval forced‐choice (2IFC) technique—a relation to be expected on theoretical grounds. The ROC's were not significantly affected by the presence of trial‐by‐trial feedback.

ISSN:0001-4966    

DOI:10.1121/1.1910779

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP