At low frequencies consideration of the quasi-static elastic moduli and densities of the gas and liquid parts of the mixture yields a value of sound velocity which is much lower than the velocity in either constituent. The computation has been confirmed experimentally in the concentration regions of 1 to 60% air by volume. The sound velocity was found from the change of phase in a plane progressive wave as a function of distance. Concentrations were determined from a measure of the hydrostatic pressure of the mixture. The “froth” was made by pumping the water rapidly past a porous glass filter through which the air was forced. A trace of detergent retarded the coalescence of bubbles. Minimum sound velocity in a water air mixture occurs at 50% concentration where the velocity is approximately 22 mps.

Calculation of Geometric Unsharpness, U_ 4 LIST OF FIGURES (continued) No. Title Page 5. Prints of a Microfocus Radiograph (Top) and a Conventional Radiograph (Bottom) of Green Ceramic Sample NB10, Showing Small Inclusions (Black Dots) 11 6. Echoes from a 3.8-mm-Thick YCrO., Sample Insonified with (Top) Longitudinal Waves and (Bottom) Shear Waves at 2.25 MHz 13 7. Sample Density vs Longitudinal Velocity of Sound for MgO + 20% Carbowax 14 8. Theoretical Upper and Lower Bounds for Longitudinal Velocity vs Carbowax Volume Fraction 15 9. Frequency Spectra for Longitudinal Waves Propagating in (A) Plexiglass and (B-D) Spinel Disks with Agglomerate Contents of (B) 0%, (C) 2%, and (D) 20% 17 10. Shear-Wave Velocity vs Applied Transducer Pressure for Silicon Nitride Greenware 18 11. Longitudinal-Wave Velocity vs Transducer Pressure for Spinel (Upper Curve) and Silicon Nitride Greenware 19 12. Phase Velocities (Dashed Curves) and Group Velocities (Solid Curves) of Longitudinal and Shear Waves as a Function of Frequency 20 13. Reference Transmission through Plexiglass 20 14. Variation of Received Longitudinal-Wave Specfum with Transducer Pressure 21 15. Comparison of Received Shear-Wave Spectra Obtained.with Transducer Pressures of 200 and 1400 kPa 21 16. Shear-Wave Spectrum for Spinel Sample NB2 21 17. NMR Image of Slices through a Water-doped SiC Disk (Axial View). . 23 18. NMR Image of Same Sample as Fig. 17 (Side View) 24 LIST OF TABLES I. Green Ceramic Specimens Used in the Present Investigation 3 II. Availability of Microfocus X-Ray Units 7 III. Sound Velocity in YCrO 3 Sample with PVA Binder 12

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are demonstrated. A simple zero c r o s s i n g c o u n t e r t o determine a n a v e r a g e frequency of t h e n o i s e spectrum y i e l d s flow rate w i t h a s t a t i s t i c a l e r r o r E where, F, i s t h e count rate and, T, t h e i n t e g r a t i o n t i m e . s two t r a n s d u c e r s are used, one r a d i a t e s s o n i c energy i n t o t h e s l u r r y . w h i c h s c a t t e r s i t t o b e rec e i v e d by t h e second t r a n s d u c e r . I n s o n i c d o p p l e r blood flowmeters p u l s e d t e c h n i q u e s a r e o f t e n used. These may have m e r i t a l s o f o r p i p e flow p r o f i l i n g , b u t are o u t s i d e t h e scope of t h i s paper.I n t h e p r e s e n t i n v e s t i g a t i o n t r a n s d u c e r s were coupled t o t h e p i p e w i t h l u c i t e wedges t o g e n e r a t e s h e a r waves i n t h e p i p e by mode conversion. F i g u r e 1 T h i s g e n e r a t o r showed s i d e bands a t l i n e frequency i n t e r v a l s of about 60 dB below t h e main s i g n a l . Without c r y s t a l s t a b l i z a t i o n t h e s i d e bands masked t h e broad band flow s i g n a l . The two curves. shown i n F i g . l , r e p r e s e n t measured a t t h e same p o i n t . t h e s i g n a l through a 0 . 1 Hz l o w p a s s f i l t e r ; o t h e rwise t h e s i g n a l i s about 1 0 dB wide a s can b e s e e n when t h e s p e c t r a are p l o t t e d on a n o s c i l l o g r a p h s c r e e n . t h e flow and no flow c o n d i t i o n s The n o i s e spectrum w a s o b t a i n e d by p a s s i n g D i f f e r e n c e S p e c t r a O s c i l l a t o r s t a b i l i t y requirements could be r e l a x e d by u s i n g a "tuned" d e t e c t o r . I n Fig. 2 t h e r e c e i v i n g t r a n s d u c e r o u t p u t i s connected, v i a a 40 dB g a i n a m p l i f i e r t o t h e RF t e r m i n a l s of t h e balanced modulator. A 0.5V s i g n a l from t h e t r a n s -S p e c t r a m i t t e r d r i v e r i s connected t o t h e LO t e r m i n a l s of A p r e l i m i n a r y s p e c t r a l a n a l y s i s f o r low veloc i t y c o n d i t i o n s showed t h e r e c e i v e d s i g n a l t o have a bandwidth of several hundred Hertz, Fig. 1. The s i g n a l i n t h i s c a s e w a s g e n e r a t e d by a c r y s t a l s t a b i l i z e d g e n e r a t o r . t h e modulator. The o u t p u t a t t h e I F t e r m i n a l of t h e modulator i s connected, v i a a 40 dB a m p l i f i e r , -291 c~i 3 4 4 -i / 7~/ 0~n n -0 E 9 l t 0 0 . 7 5 0 1978 I E E E

The complex sound-propagation constant is calculated for liquid-vapor mixtures. At low frequencies, the sound velocity is a function of the mixture quality or relative masses of the phases. At intermediate frequencies, the propagation depends on the sound frequency and also on the size distribution of the discontinuous phase. At high frequencies, the propagation is essentially a function of the predominant phase. Calculations at intermediate frequencies lead to complicated expressions for the wave-propagation constants. This is true even for an idealized 2-phase fluid as, for example, a vapor fog containing uniformly dispersed droplets of equal size. Simplified expressions taking into account drag and heat transfer between the phases yield estimates of the relaxation times or time constants associated with these processes. These time constants determine the region of frequency and aggregate sizes of the individual phases in which these parameters have little effect on the propagation constants. [Work supported by the National Aeronautics and Space Administration.]

The output of a 32-kc/sec laminated nickel-bar magnetostrictor radiating from each end into long 0.275 i.d. oil-filled pipes was monitored with a Kistler 601 gauge, as a function of the hydrostatic pressure applied to the system. The output of the magnetostrictor increased monotonically over the pressure range: 0–150 atm. Corrections for medium density and impedance change were applied but proved to be small. Brass masses attached to the ends of the magnetostrictor were adjusted to minimize interaction with modes of vibration other than the desired fundamental longitudinal mode. These masses also acted as pistons fitting loosely in the ends of the pipes. [This work was sponsored by the U. S. Office of Naval Research.]

Earlier suggestions to reconcile the observed broad frequency-displacement function of the basilar membrane and the subjective high discrimination of the hearing mechanism seek an explanation in possible neural interaction and mutual suppression of less strongly stimulated neurons in the vicinity of more strongly stimulated neighbors. This explanation leaves questions on the hearing of combinations of tones in doubt. A mechanism is postulated based on the traveling-wave nature of the disturbance of the membrane. In the vicinity of the maximum of the displacement, the wavevelocity of the disturbance on the membrane is a sharp function of frequency. Many hair cells are assumed to be excited in phase with the local displacement, and signals passing from a receptor closer to the stapes are delayed in time with respect to the signal from the more apical receptors. Delays due to neuron pathlength are assumed to be an exact replica of the time delay of the signal along the membrane, for a specific frequency. Different delay-line characteristics in a given region of the membrane would, therefore, produce simultaneity of pulses at separate synapses for slightly different frequencies. Plausibility of this hypothesis is greatly enhanced by the observation that the phase velocity of the traveling wave on the basilar membrane at the point of maximum displacement is very close to the velocity of signals along unmyelinated nerve fibers, so that the latter could act in exactly the manner postulated. [This work was supported by the Electromagnetic Warfare and Communications Laboratory, Aeronautical Systems Division.]

Transition to turbulence was observed in water flowing in a narrow rectangular channel provided with a flexible interface by making use of measurements of instantaneous velocity, as indicated by a deposited-film constant-temperature anemometer. The characteristics of the transition from laminar flow near the entrance of the channel to the fully turbulent condition downstream may be described as consisting of a series of random bursts of flow fluctuations separated by steady-flow conditions. The number of turbulence bursts in unit time interval increases monotonically on a sigmoid curve in the transition region. A measure of the degree of turbulence based on a counting technique was developed for this study. Transition to turbulence sets in earlier for some types of flexible surfaces than it does for rigid walls. However, the rate of increase was greatest for the rigid walls. [This work was sponsored by the David Taylor Model Basin.]