摘要:

This paper presents a fairly complete review of detection theory as it is applied to certain psychoacoustic data. Detection theory is treated as a combination of two theoretical structures: decision theory and the concept of ideal observer. The paper discusses how statistical decision theory has been used to analyze the auditory threshold process. By treating the threshold process as an instance of hypothesis testing, two determinants of the process are recognized: (1) the detectability of the signal and (2) the criterion level of the observer. The theory provides a technic of analysis which allows one to obtain a quantitative estimate of both factors. The measure of signal detectability appears to be independent of the psychophysical procedure when the physical parameters of signal and noise are held constant. The concept of ideal observer is reviewed with special emphasis on the assumptions of the derivation. The usefulness of this concept is illustrated by considering the shape of the psychophysical function—the function relating the detectability of the signal to its intensity. A rather general model based on the concept of signal uncertainty is presented which attempts to explain this relationship.

ISSN:0001-4966    

DOI:10.1121/1.1907882

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

The near‐ and far‐field noise from the turbulent boundary layer developed on a rotating cylinder has been studied; both smooth and artificially roughened surfaces were employed. The cylinder walls were sufficiently thick to inhibit appreciable boundary‐layer‐excited vibration noise. The mean square pressure followed aU4law in the near field, and the total acoustic power radiated to the far field followed a higher exponent law: approximatelyU6. The necessity to excise spurious peaks at harmonics of the cylinder speed from the measured far‐field spectrum introduced inaccuracy in the computed power law, bringing some doubt to bear on the accuracy of the exponent. TheU6law, unless it is a fortuitous average of laws of lower and higher power, suggests that the dominant radiators are of a dipole type. Drag calculations from hot‐wire measurements allowed an estimate of the efficiency (acoustic power/mechanical power) of the far‐field radiation, resulting in an efficiency of the order of 30 times that for the quadrupole radiation from a jet at a Mach number of 0.228. Even so, the measured noise power from the boundary layer over arigid wallappears to be relatively small in any practical application to the noise in aircraft. This is in contradistinction to the noise radiated by boundary‐layer‐induced vibrations of a flexible wall or panel which can exceed the former by some orders of magnitude.

ISSN:0001-4966    

DOI:10.1121/1.1907883

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

Oxyhemoglobin in dilute aqueous solution is rapidly converted by ultrasonic irradiation into methemoglobin, which in turn is gradually destroyed, as shown by the disappearance of its optical absorption peak at 4050 A. Hematoporphyrin similarly suffers partial destruction by ultrasound. On the basis of experiments in various chemical environments, the previous results are ascribed largely to the nitrous and nitric acids produced by ultrasonic cavitation in water containing dissolved air. Adding 0.1 ml ether/25 ml of solution causes the sonochemical change to be from oxyhemoglobin into carboxyhemoglobin, instead of into methemoglobin. Ultracentrifuge studies indicate that ultrasonic treatment of hemoglobin in more concentrated solution also causes some splitting off of the heme from the globin. A comparison of the reported effects of x rays on hemoglobin with those found for ultrasound shows that there are differences as well as similarities. The ultrasonic frequency used was 400 kc per sec, and the acoustic power delivered into the reaction vessel in a focused beam was about 20 w.

ISSN:0001-4966    

DOI:10.1121/1.1907884

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

A simple method, based on the total reflection of a sound beam from a liquid‐solid boundary at the critical angles, is described. With this method, it is possible to measure the velocity of longitudinal and shear waves in thesolidby locating the angles of maximum reflection in theliquid.

ISSN:0001-4966    

DOI:10.1121/1.1907885

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

An ultrasonic interferometer, consisting of a barium titanate ceramic cylinder suspended in a high‐pressure vessel, has been used to measure the velocity of sound in liquid argon and liquid nitrogen at temperatures near their boiling points and at pressures up to 135 atm. The apparatus is suitable for measurements at much higher pressures, since it is rugged, compact, and has no moving parts. An analysis of the resonances obtained over a frequency range 0.2f0to 1.7f0(wheref0is the thickness resonant frequency of the ceramic cylinder) has shown that a simple relation exists between the velocity in the liquid and the zeros of the Bessel functionsJ0andJ1for frequencies near 0.5f0and 1.5f0. The velocity data obtained agree with previous measurements on liquid argon and liquid nitrogen at atmospheric pressure, but show that the velocity of sound in these liquids is not a linear function of pressure, as had been supposed by Itterbeek. Using known density data, the adiabatic compressibility and ratio of the specific heats γ have been found for liquid argon and liquid nitrogen at 90°K. For argon, γ falls slightly from 1.97 to 1.89 as the pressure rises to 135 atm, but for nitrogen γ rises from 1.50 to 1.79 with the applied pressure, suggesting the hindering of intramolecular motions at the higher pressures.

ISSN:0001-4966    

DOI:10.1121/1.1907886

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

Ultrasonic measurements of the longitudinal absorption and velocity and shear impedance were made over a large range of temperatures in the weakly associated liquid isobutyl bromide. Evidence was found for the coexistence of four different relaxation mechanisms. Above −50°C rotational isomeric relaxation exhibiting a single relaxation time was found. Vibrational relaxation also appears to be present with a relaxation time shorter than that usually found in nonassociated liquids. The dispersion and absorption data below −125°C showed that both shear and structural relaxation effects were present. The former was related to a distribution of relaxation times. The coexistence of these several relaxations is consistent with the concept that a weakly associated liquid should show relaxation behavior typical of both strongly and nonassociated liquids.

ISSN:0001-4966    

DOI:10.1121/1.1907887

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

Observations have been made of a thin rectangular jet which issues from an orifice and impinges upon the apex of a rigid wedge which is parallel to the plane of the jet. Such a system displays steady motion or motion corresponding to one of a unique set of ordered oscillatory modes. Which state of motion occurs at a given time depends upon stream thickness, orifice‐to‐edge distance, stream velocity, kinematic viscosity, and the previous history of the jet. The investigation is divided into two main parts. One deals with the ranges of parameters of the system for which it will execute self‐maintained oscillations of a given mode; the other treats frequency characteristics for the different modes. It is found that self‐maintained oscillations exist in fluids with a wide range of viscosity. The frequency characteristics are obtained by both optical and acoustical methods; an empirical formula for the frequency is developed.

ISSN:0001-4966    

DOI:10.1121/1.1907888

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

An experimental arrangement is described which permits controllable generation of small‐scale acoustic streaming, i.e., “microstreaming” near a plane boundaryS. This arrangement, which consists essentially of a cylindrical bar oscillating longitudinally above the boundarySin question, has been used in studies of sonically‐produced effects at a fluid‐solid interface. The present paper deals with first‐order pressure and velocity fields in the thin layer of fluid betweenSand the vibrating face of the bar. Theoretical expressions are developed, based on a simple model in which incompressible flow is assumed. Experimental determination of the pressure field was accomplished by means of a special hydrophone arrangement described herein, which measures the pressure at points along the plane boundary. The first order theory agrees well with experiment, and is thus judged satisfactory as basis for a detailed treatment of the microstreaming flow, to be given in a subsequent paper. A byproduct of the work is a method for calibration of small hydrophones.

ISSN:0001-4966    

DOI:10.1121/1.1907889

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

The response of a solid subjected to intense blast pressures depends on the ratio of the applied pressures to the stresses (yield stress, etc.) characteristic of the material of the solid. When this ratio is small, the solid can be expected to respond elastically. The paper develops the elastic theory of a semi‐infinite solid exposed to a blast initiated at a point on the surface, assumed to be in air at sea level. The results are explicit expressions for the displacements and stresses for early time, small radial distances, and shallow depths. Application to the case where the solid represents the earth is discussed.

ISSN:0001-4966    

DOI:10.1121/1.1907890

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

An earlier paper by the author considered the behavior of a semi‐infinite solid reacting elastically to a point‐initiated blast wave at the surface. When the applied pressures are sufficiently high, the solid will experience inelastic behavior characteristic of the material. The earth is here regarded as a medium made up of solid matter, water, and air voids. It is assumed that the principal effect of high normal stresses is to close up the air voids and that thereafter the medium acts like an elastic solid. The calculation of the peak pressure vs depth is compared with experimental data derived from nuclear bomb tests and shows reasonable agreement considering the wide scatter of test points.

ISSN:0001-4966    

DOI:10.1121/1.1907891

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP