Volume 122, Issue 4, October 2007
Index of content:
- ULTRASONICS, QUANTUM ACOUSTICS, AND PHYSICAL EFFECTS OF SOUND 
122(2007); http://dx.doi.org/10.1121/1.2767419View Description Hide Description
-plutonium’s volume-corrected polycrystalelastic moduli were measured between and the upper limit of its occurrence, near . The two independent moduli for a polycrystal—bulk and shear—behave smoothly, indicating no phase transition. Both moduli show the same 50% increase on cooling, an order of magnitude larger than in other metals. The Debye temperature obtained from low-temperature elastic moduli,, significantly exceeds most previous estimates. The Gruneisen parameter , obtained from the temperature dependence of the bulk modulus, is intermediate among previous estimates using other approaches, -plutonium’s Poisson ratio is low: 0.18, nearly temperature independent, and its small decrease on warming opposes usual behavior. The high , large but equal bulk modulus and shear modulus fractional stiffening on cooling, and near-temperature-invariant are attributed to a single mechanism: electron localization—delocalization.
122(2007); http://dx.doi.org/10.1121/1.2773991View Description Hide Description
Research on cavitational bioeffects of diagnostic ultrasound (DUS) typically involves a diagnostic scanner as the exposure source. However, this can limit the ranges of exposure parameters for experimentation. Anesthetized hairless rats were mounted in a water bath and their right kidneys were exposed to ultrasound. Amplitude modulation with Gaussian envelopes simulated the image pulse sequences (IPSs) produced by diagnostic scanning. A IV dose of contrast agent was given during exposures. Glomerular capillary hemorrhage was assessed by histology. A stationary exposure approximated the bioeffects induced by DUS within the beam area. However, the use of five closely spaced exposures more faithfully reproduced the total effect produced within a DUS scan plane. Single pulses delivered at intervals induced the same effect as the simulated DUS. Use of triangle-wave modulations for ramp-up or ramp-down of the IPS gave no effect or a large effect, respectively. Finally, an air-backed transducer simulating DUS without contrast agent showed a zero effect even operating at twice the present DUS guideline upper limit. Relatively simple single-element laboratory exposure systems can simulate diagnostic ultrasound exposure and allow exploration of parameter ranges beyond those available on present clinical systems.
Wigner distribution of a transducer beam pattern within a multiple scattering formalism for heterogeneous solids122(2007); http://dx.doi.org/10.1121/1.2773989View Description Hide Description
Diffuse ultrasonic backscatter measurements have been especially useful for extracting microstructural information and for detecting flaws in materials. Accurate interpretation of experimental data requires robust scattering models. Quantitative ultrasonicscattering models include components of transducer beam patterns as well as microstructural scattering information. Here, the Wigner distribution is used in conjunction with the stochastic wave equation to model this scattering problem. The Wigner distribution represents a distribution in space and time of spectral energy density as a function of wave vector and frequency. The scattered response is derived within the context of the Wigner distribution of the beam pattern of a Gaussian transducer. The source and receiver distributions are included in the analysis in a rigorous fashion. The resulting scattered response is then simplified in the single-scattering limit typical of many diffuse backscatter experiments. Such experiments, usually done using a modified pulse-echo technique, utilize the variance of the signals in space as the primary measure of microstructure. The derivation presented forms a rigorous foundation for the multiple scattering process associated with ultrasonic experiments in heterogeneous media. These results are anticipated to be relevant to ultrasonic nondestructive evaluation of polycrystalline and other heterogeneous solids.