摘要:

Two noncollinear pump modes of 5 and 7 MHz have been excited in an isotropic plate of brass. For certain pump‐mode configurations, the pump modes could interact via the nonlinearities of the medium to produce a third Lamb mode at the sum frequency of 12 MHz. The three‐phonon interaction has been detected using an optical probe for two pump‐mode configurations. pressure,discharge energies, and translational temperature of the

ISSN:0021-8979    

DOI:10.1063/1.325184

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Ultrasonic attenuation has been measured for a range of ceramic polycrystals. An extreme‐value approach for attenuation analysis has been developed, based on numerical scattering cross sections and an extreme‐value characterization of the microstructure. A good correlation between predicted and measured attenuation has been obtained in each case. The implications of the analysis for ultrasonic failure prediction and microstructural characterization have been explored.

ISSN:0021-8979    

DOI:10.1063/1.325185

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Acoustic resonances were observed in high‐pressure (600 Torr) sodium‐mercury‐xenon discharges operated with ac input at power frequencies of 2–120 kHz. Three sizes of cylindrical sapphire arc tubes were operated at constant average powers of 400, 250, and 150 W, respectively. The observed resonance frequencies and arc shapes agree well with a simple analysis of standing pressure waves in cylinders. The results indicate that transverse resonances effectively average the gas temperature across the arc, while longitudinal resonances mainly involve the hot core of the discharge.

ISSN:0021-8979    

DOI:10.1063/1.325186

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Expressions are developed for the internal efficiencies of magnetoelastic Rayleigh‐wave convolvers. A bulk‐wave formalism is used to express the nonlinear magnetization componentsmresponsible for the convolution, as the square of the input signalsS1andS2, i.e.,m=&eegr; (S1+S2)2. The resulting expressions for &eegr; have a resonance‐type denominator of the form &ohgr;2−&ohgr;20, where &ohgr;0is the gyrofrequency. Such a resonance does not occur with surface magnetoelastic waves. The results are adapted to the surface‐wave case by means of an approximation to estimate the nonzero value of the denominator. Experimental values of &eegr; range from 1.2×105to 4.7×105Wb/m2for the best convolvers reported to date. Corresponding theoretical values range from 9.5×104to 1.58×105Wb/m2. Uncertainties in the experimental and theoretical estimates are discussed.

ISSN:0021-8979    

DOI:10.1063/1.325187

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A set of plasma rate equations are obtained which describe the time evolution of the electron density and temperature for an rf discharge in a magnetic field. Numerical solutions to these equations have been obtained for argon at pressures of 0.1–100 mTorr using the classical rf conductivity as the mechanism for transferring energy from the rf field to the electrons, and ambipolar diffusion and disassociative recombination as the dominant loss mechanisms. The typical temperature solution exhibits two well‐defined temperature plateaus. The electron‐density solution exhibits a monotonic growth to a saturation value which constitutes an appreciable percentage of the initial neutral‐particle density. At the higher pressures, such large amounts of power are required to maintain the saturation density that source power may be the principle limitation on the maximum density achievable in the typical rf plasma source.

ISSN:0021-8979    

DOI:10.1063/1.325188

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Reflection of an obliquely incident impulsive plane electromagnetic wave from lossless, cold, isotropic, and uniaxial plasma half‐spaces moving perpendicular to the plane of incidence is considered. The analytical solutions are obtained by inversion of the appropriate Laplace transforms. The analysis shows that in the case of uni‐xplasma both the pulse height and loop width of the reflected field decrease with increase in the medium velocity. However, in the case of uni‐yplasma (perpendicular polarization) the pulse height decreases and loop width increases with increase in the medium velocity. Also, some more results are presented and discussed in the text.

ISSN:0021-8979    

DOI:10.1063/1.325189

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Although Thomson scattering of laser light from plasmas has become a widely accepted laboratory diagnostic technique, many experiments involving high‐density low‐temperature plasmas suffer from a masking of the incoherent scattered radiation by bremsstrahlung radiation and by reflected and refracted light signals; consequently, few accurate measurements have been made on laser‐produced plasmas. To a large extent these disadvantages have been removed from the present work wherein a high‐density (∼1019/cm3) low‐temperature (∼10–15 eV) plasma has been generated in 300‐Torr pressure of helium by a 3‐J CO2TEA laser, while scattering measurements have been performed with a separate pulsed ruby laser system operating at 0.15 J. Specifically, the frequency spectrum of the incoherent light scattered at 90° from the plasma has been obtained allowing temperatures to be measured in the plasma with a spatial resolution of 250 &mgr;m. Holographic interferograms have also been obtained. From the central‐ion feature of the scattered‐light spectrum, the plasma was inferred to be in thermal equilibrium with equal electron and ion temperatures. The maximum value of the temperature is 17 eV±11&percent;. Additionally, the value of the electron number density from scattering measurements and that found from plasma holograms differ by less than 30&percent;. The scattering results agree well with theoretical predictions for scattering from thermal fluctuations in an equilibrium plasma. The experiment also shows that the calculated values for bremsstrahlung emission approach the observed plasma noise for electron densities near 1019/cm3, but that other noise sources determine the signal‐to‐noise ratio at lower number densities. The techniques of this paper can be used to study nonequilibrium plasmas where instabilities dominate the scattered‐light spectrum.

ISSN:0021-8979    

DOI:10.1063/1.325190

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The first two orders of parametric interaction between two plane Alfve´n waves propagating in opposite directions in a spatially uniform inviscid perfectly conducting fluid pumped by a plane progressive sound wave are investigated for the case in which all three waves propagate parallel to the uniform magnetic flux permeating the fluid. The Alfve´n waves become evanescent or absolutely unstable depending on the value of the sound wave velocity relative to the Alfve´n wave velocity. The important charactristics of the evanescence and the absolute instability have been deduced.. Also, the amplitude‐dependent frequency and wave‐number shifts of the center of the second‐order parametric interaction region have also been determined.

ISSN:0021-8979    

DOI:10.1063/1.325191

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Repeated heat treatments at 1100 °C on CZ‐grown wafers result in the nucleation and growth of stacking faults in the vicinity of oxygen precipitates. During the high‐temperature treatment, the precipitates and the stacking faults grow. During the cooling, new precipitates form on the SF bounding partial which by their subsequent growth can generate a ring‐shaped stacking fault on top of the first one. Possible mechanisms involve interstitial condensation at the SF partial or vacancy generation by the partial climb. Models of the growth kinetics are discussed and take into account both mechanisms.

ISSN:0021-8979    

DOI:10.1063/1.325192

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Single crystals of silicon containing prediffused arsenic, boron, and phosphorus profiles are bombarded at 600–900 °C with 250–360‐keV protons. Under conditions approaching ideality (low impurity concentration and less than 1013protons/cm2 sec) enhanced impurity diffusion appears to proceed in an uncomplicated manner which is well described by steady‐state kinetic treatment. At high temperatures and very low bombardment fluxes the enhanced‐diffusion coefficients are observed to be temperature independent and first‐order dependent upon flux. At moderately increased damage rates, particularly at lower temperatures, the diffusivities become temperature dependent and a half‐order flux dependence is observed. The results are explained by assuming proton‐enhanced diffusion to be controlled by the migration of split monovacancies (semivacancy pairs). Consistency with annealing studies of radiation‐induced defects at much lower temperatures and with thermally activated diffusion studies at higher temperatures is attained by assuming a 1.47‐eV migrational enthalpy and a 3.66‐eV enthalpy of formation for the uncharged defect.

ISSN:0021-8979    

DOI:10.1063/1.325193

出版商:AIP    

年代:1978

数据来源: AIP