摘要:

Sound speeds were measured from 2 to 32 amagats in sulfur hexafluoride at 26°C by spontaneous Brillouin scattering. The observed dispersion can be accounted for entirely by the nonideality of the gas. It is concluded that vibrational contributions to the specific heat are completely relaxed. No evidence of rotational relaxation was observed. Comparison of these data by commonly used techniques with those determined from ultrasonic measurements is shown to be inadequate in the case of sulfur hexafluoride for the densities used. Comparison can be made using the exact thermodynamic equation and assuming relaxing specific heat. The difference between the smoothed experimental results and the exact calculated values is less than 0.7% over the density range studied.

ISSN:0001-4966    

DOI:10.1121/1.1913247

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

The Greenspan rule for calculating the combined absorption of sound in polyatomic gases from the separate values of the classical and internal absorption is extended to include the effects of more than one internal degree of freedom. Comparison is made between the results of absorption calculations based on this generalization and those obtained from the simple addition rule and the 17‐moment theory.

ISSN:0001-4966    

DOI:10.1121/1.1913248

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

Previous values of the vibrational relaxation time of pure oxygen determined from acoustic absorption measurements in the pressure range 14–35 atm showed the pressure dependence to be other than that expected from binary collisions alone. Over this pressure range, values of the inverse relaxation time could be represented as the sum of a linear and quadratic pressure term. This paper describes results obtained by extending the pressure range to 55 atm. It is found that the data cannot be interpreted solely on this basis. A study of the effect of imposing a strong magnetic field at the highest pressure showed no effect.

ISSN:0001-4966    

DOI:10.1121/1.1913249

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

It is proposed that amplification of phonons of frequencies in the order of hundreds of gigahertz can be investigated by measuring expected changes in the free carrier absorption coefficient which will occur from changes in the density of thermal phonons. It is shown that for photon energies greater than the thermal energy, there is a one‐to‐one correspondence between the energy of the incident photons and the momentum of the phonons that are required for free carrier absorption by means of intraband electron transitions. An important result derived is that the phonon energy per unit bandwidth, at a particular phonon frequency proportional to the incident radiation energy, is directly related to the ratio of the free carrier absorption coefficients during and before acoustoelectric amplification. As a specific example, the case ofCO2laser radiation absorption inn‐type Ge is considered, leading to the result that at 10 K the free carrier absorption coefficient will increase by several orders of magnitude over its thermal equilibrium value during acoustoelectric amplification. In addition, the dependence of the free carrier absorption coefficient on the phonon density suggests applications in some laser devices such as photon drag detectors and amplitude modulators.

ISSN:0001-4966    

DOI:10.1121/1.1913250

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

The basic equation for propagation of sound‐wave pulses through a turbulent atmosphere moving with a mean wind has been obtained from first principles. The general solution of the basic equation has been found and expressed in a form simple enough to permit application to the analysis of problems of prediction and interpretation of data obtained from the various types of acoustic sounder experiments, including power spectra, intensity spectra, and cross sections for both backscatter and forward‐scatter configurations.

ISSN:0001-4966    

DOI:10.1121/1.1913251

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

Acoustic refraction by atmospheric wind and temperature inhomogeneities affects the measurements of acoustic sounders in four ways: (a) It displaces the location of the scattering volume relative to its apparent location based on straight‐line ray paths. (b) It alters the magnitude of the Doppler shift by changing the magnitude and direction of the wave vector at the scatterer. (c) It changes the scattering angle from that based on a straight‐line geometry. (d) It introduces Doppler‐shift contributions due to time variations of the atmospheric refractive index all along the sounding path. An idealized model of all these effects on bistatic soundings shows that most refractive corrections are small for present sounding geometries up to heights of about 1 km, but may need to be accounted for as sounding heights increase.

ISSN:0001-4966    

DOI:10.1121/1.1913252

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

The method of matched asymptotic expansions is used to obtain an asymptotic solution to the Helmholtz equation for the problem of an open‐ended duct. The small expansion parameter ε is given by the ratio of the duct openingHto the duct characteristic length scaleL. Three separate asymptotic expansions are needed to describe the solution, one valid in the duct interior, one valid at the duct edge, and one valid in the free‐space exterior region. Asymptotic matching shows that the asymptotic series must contain terms such as ε logε. Finally, results are cast in the form of a duct terminal impedance and compared with an exact solution for a parallel‐sided duct.

ISSN:0001-4966    

DOI:10.1121/1.1913253

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

A two‐dimensional detailed study of the behavior of long waves in curved ducts and in junctions between straight and curved ducts will be given. The mathematical treatment of the problem utilizes the method of separation of variables. Solutions and expressions for principal mode of the wave are obtained by using the linearized equation of motion solved for its characteristic values. The unavoidable approximations in the numerical solutions of the cylindrical functions are due to use of series expansion of Bessel functions and from restrictions necessary to solve infinite matrices.

ISSN:0001-4966    

DOI:10.1121/1.1913254

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

The results of a theoretical and experimental study of the elastic strain produced in a cylindrical bar by a moving step function load on the lateral surface are presented. A double transform technique is used to solve the problem of determining the elastic strain produced by both normal stress loading and shear stress loading on the lateral surface of the bar. The exact solution is given as a sum of Fourier integrals, all but one of which are identified as Pochhammer‐Chree waves. The additional Fourier integral represents a mode of elastic wave propagation which is nondispersive and has a phase velocity equal to the lateral surface loading velocity. Asymptotic solutions to the Fourier integrals are obtained and compared with experimental strain‐time records. When corrections are included for electrical circuit response and viscoelastic effects, the predicted strain‐time curves fall within the experimental error associated with the records. Strains were measured using thin film strain gauges embedded in a plexiglas bar. The bar was loaded by a plane air shock.

ISSN:0001-4966    

DOI:10.1121/1.1913255

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

A plane‐strain investigation of the dynamic stability of an infinitely long cylindrical shell undergoing breathing oscillations in an infinite inviscid fluid medium is presented. Kinematic nonlinearities of the shell are retained while the fluid is regarded as a linear acoustic medium. A stability criterion which depends strongly upon the acoustic reactance is developed. When the shell is immersed in a fluid, the added mass of the fluid reduces the frequency for parametric resonance. The damping provided by the acoustic resistance proves to be negligible at parametric resonance. The validity of the neglect of kinematic nonlinearities of the fluid is demonstrated by means of an example.

ISSN:0001-4966    

DOI:10.1121/1.1913256

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP