摘要:

The ultrasonic irradiation of water was effected under an argon atmosphere with an 800‐kHz transducer at several intensities. The rates of hydrogen peroxide formation were followed by spectrophotometric analyses. The results were utilized to relate intensity to reaction rate for standardization purposes. Irradiations of several alkyl amines in aqueous solution or suspension were next accomplished under conditions similar to those applied to pure water. Products included aldehydes, an alcohol, amines, anN‐oxide, methane, ethane, ethylene, carbon monoxide, and hydrogen. The products and their ratios were dependent on the structure of the amine used in the reaction. Reaction rates were only slightly different when an oxygen atmosphere was used instead of argon. The reactivity order for the amines was observed to be primary>secondary>tertiary. Methylamines reacted somewhat faster than didn‐butylamine.

ISSN:0001-4966    

DOI:10.1121/1.1903465

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

An immersion apparatus for making ultrasonic measurements in polymers was constructed. A unique feature of this apparatus is that the specimen is held vertically, and the transducers are rotated in order to produce shear waves in the specimen. This arrangement allows measurements to be made through the melting point of crystalline polymers. Sound‐speed measurements, accurate to ±2%, were made on 25 polymers at room temperature and on five of these polymers as a function of temperature. On 15 of the polymers, both longitudinal and shear sound speeds were measured. The longitudinal wave speeds ranged from 2820 to 1020 m/sec, while shear wave speeds ranged from 1230 to 650 m/sec. Using these sound speeds and measured densities, the elastic constants of these polymers were calculated. For four polymers elastic constants as a function of temperature were calculated.

ISSN:0001-4966    

DOI:10.1121/1.1903466

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Experiments were conducted to investigate the scattering of a wide bandwidth pulse by a fluid‐filled cylindrical cavity in an elastic solid. The pulse amplitude‐time record and the corresponding Fourier power spectra of the scattered pulses are analyzed. The sequence of pulses received by a transducer is identified by applying the theory of geometric acoustics and the pulse arrival times are related to the cavity diameter and the wave speed in the fluid. The power spectrum is interpreted in terms of the resonance of the fluid inclusion, the natural frequencies of which also depend on the size and property of the inclusion. Investigations show that both pulse‐time record and power spectrum can be utilized to detect the size and the wave speed of a fluid inclusion in a solid.

ISSN:0001-4966    

DOI:10.1121/1.1903467

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

A method for the analysis of vibration of shallow shells is presented. The method is based upon the concept of iso‐amplitude contour lines on the vibrating surface of the shell. The problem of transient axisymmetric vibrations of shallow elliptical dome is investigated. It is shown that in the limiting case, when the elliptical dome reduces to the spherical dome, Reissner's well‐known result is obtained.

ISSN:0001-4966    

DOI:10.1121/1.1903468

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Reactive mufflers withNresonant chambers but with constant total muffler volume and total internal piping length are studied. The ratio of outflow to inflow for periodic inflow is studied as a function of frequency. It is shown that, although the sharpness of the high‐frequency attenuation is increased by increasing the number of resonant chambers, the cutoff frequency and the highest resonant frequency also increase.

ISSN:0001-4966    

DOI:10.1121/1.1903469

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

NEF contours for aircraft noise have generally been computed assuming three or four well‐defined flight paths from a given runway. In fact, a whole continuum of flight paths normally exists. In this paper, methods are developed to treat this continuum of flight paths. Simplifications are also suggested which provide realistic approximations and which allow preliminary calculation of NEF values without the need for major computer programming. These have the form NEF = NEFC + correction, where NEFC assumes all flights are overhead, and a (negative) correction term is added for the splayout. Results of the conventional discrete path computations are contours shaped like fingers. Using a continuous spread of paths results in a single fanned‐out contour. We feel the latter is more realistic.

ISSN:0001-4966    

DOI:10.1121/1.1903470

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The phenomena of background noise generation in transonic wind tunnels are analyzed. In unsteady aerodynamic tests, background disturbances create problems because the instrumentation senses them in addition to the fluctuations generated by the aerodynamic flow over wind‐tunnel models. Calibrations of 25 facilities show that the amplitudes of the background fluctuations are excessive. In porous‐wall facilities, one noise source consists of porous‐wall edgetones that are generated by the passage of air over the holes. A flow model is developed that yields the frequencies of these oscillations. Test section boundary layers and hole configurations govern the occurrence of these fluctuations. In slotted‐wall facilities, a noise source is the slotted‐wall shearing caused by the air flowing along the openings. In both types of wind tunnels, other flow mechanisms also cause disturbances, and these phenomena are described. Noise‐reduction methods are outlined which will provide valid unsteady aerodynamic results.

ISSN:0001-4966    

DOI:10.1121/1.1903471

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

A graph and an equation are presented for the ready evaluation of the required sound‐transmission loss at any frequency for each of several components of a composite sound barrier, to economically achieve a desired interior noise spectrum, given the spectrum of the exterior noise and the areas of each of the significant boundaries of a room. It is also established that for common automobile and jet aircraft noises, the necessary insulation of such exterior room boundaries is not well represented by an STC rating.

ISSN:0001-4966    

DOI:10.1121/1.1903472

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

In an effort to provide guidelines for law enforcement personnel to protect their hearing, the peak pressure level and signal duration (AandBduration) of eight popular firearms were measured and compared with the requirements of OSHA (1970), CHABA DRC (1968), and EPA levels (1974). Small condenser microphones and a storage oscilloscope were used to record the blast wave signatures from a 9‐mm automatic, 0.357‐cal. Magnum revolver, 0.41‐cal. Magnum revolver, 0.22‐cal. revolver, 0.45‐cal. automatic, 0.44‐cal. Magnum revolver, 12‐gauge shotgun, and 0.22‐cal. rifle. Measurements were made at the ear of the person shooting and at the approximate position of a neighbor at a firing range. Some measurements were also made at a practice firing range. A portable tape recorder was found useful for recording gun signals and measuringBdurations. The peak pressure levels of the signatures of all the firearms tested exceed the OSHA maximum of 140 dB. It was found that in an anechoic environment the noise from five of the handguns exceeded the CHABA DRC (1968), while the noise from all of the firearms tested, except the 0.22‐cal. rifle, exceeded the EPA levels (1974). At a sound‐insulated firing range, the noise from all the firearms tested, except the 0.22‐cal. rifle, exceeded the CHABA DRC (1968), while all the firearms tested exceeded the EPA levels (1974).

ISSN:0001-4966    

DOI:10.1121/1.1903473

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

An analysis of the transmission of sound through sandwich panels (consisting of lightweight, flexible cores between relatively stiff skins) is presented here. First, previously given results for the free vibrations of such panels are analyzed and unified. Then, a traveling‐wave analysis is used to obtain impedances and transmission‐loss formulas, which are in turn compared with previously published experimental data. The comparison is relatively good, and confirmation of a symmetric coincidence effect is obtained. Further, the numerical results indicate that this symmetric coincidence generally occurs at a much lower frequency than does antisymmetric (shear wave) coincidence.

ISSN:0001-4966    

DOI:10.1121/1.1903474

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP