When an oscillating piston forces the enclosed gas in a Kundt tube to vibrate with a finite amplitude near an acoustic resonance frequency of the gas column, shock waves are generated which travel periodically back and forth in the tube. There is also heating of the gas and a rise in its mean pressure. In this paper a theory of the steady state motion of the gas in its “fundamental” mode has been devised which includes the dissipative effects of wall friction and heat conduction to the tube walls. The dependence of shock strength, mean temperature, and mean pressure on piston amplitude, tube length, gas viscosity, and heat conductivity predicted by the theory are in good qualitative agreement with the small number of experimental data available at present.
With x and y log-transformed fish standard length/and equivalent swimbladder radius R, respectively, probability density distributions p(x,y) for mesopelagic swimbladdered fish species are assumed to be bivariate normal. From archival measurements, models are developed for 36 nonregressive species, 2 regressive species, and selected species groups found off Bermuda. Statistical tests suggest the hypothesis is valid for many of these species, and that failures are due largely to small sample variability and bias in the available data. Marked differences between regression, major axis, and reduced major axis allometric exponents, which sometimes occur when x,y correlation is low, are explained. A dimensionless allometric law R′* = k* (l′*)m involving structural variables l′* and R′* scaled to lmax is used to compare specific swimbladder growth trends. Major axis estimates of m* and k* for the nonregressive species group are each lognormally distributed with respective means [Formula: see text] and [Formula: see text]. A structural relation model for this group based on the hypothesis that swimbladder wall area grows approximately as the first power of fish volume or mass is verified. Last, detailed buoyancy properties are calculated for 6 nonregressive species with bivariate normal (x,w*)-distributions, where w* is the logarithm of percentage swimbladder volume.
Background noise spectra from 11–250 cps have been obtained in a deep inland lake in the absence of wind, waves, shipping, and marine life. An upper estimate of the spectrum level is given. It is 10 db lower than that of the Knudsen zero sea-state curve and its extrapolation to 11 cps. Measurements were also made of the variation in time of the spectrum under moderately rough surface conditions. From 90 to 250 cps the spectrum appears to be generated by the wind, and there is no significant depth effect at these frequencies over the depth range 68–244 ft. This report also discusses special instrumentation problems in the measurement of very low-level, nonstationary ambient noise.
The bistatic scattering strength S(φi,φs) = 10 logs (φi,φs) of the ocean surface has been measured in 12-oct bands over the frequency range 62.5–4000 Hz for a wide range of grazing angles of incidence and scattering, φi and φs. Explosive charges at the bottom of a vertical string of hydrophones were used to ensonify the surface. Concurrent measurements of surface roughness were taken with an accelerometer float. S was obtained for rms waveheights Ĥ between 1.9 and 2.8 ft and rms omnidirectional slopes tanΘ̂ between 0.10 and 0.13. For frequencies between 62.5 and 1440 Hz, the bistatic scattering coefficient s may be represented in the form s=CeD[sinφi+sinφ2]2, where C and D are functions of the surface roughness parameters kĤ and tanΘ̂. The functions have one form when surface shadowing of the scattered radiation is weak (φi > Θ̂, φs > Θ̂), and another form when surface shadowing is strong (φi > Θ̂, φs ⪅ Θ̂).
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