Theory for acoustic propagation in materials which can support stress and which contain gas bubbles, with applications to acoustic effects in marine sediment and tissue

Whilst there is a considerable body of work in the literature on the theory of acousticpropagation in marine sediment, the incorporation of gas bubbles into such theories isdone with the inclusion of assumptions which severely limit the applicability of thosemodels to practical gas-laden marine sediments.Section 2 develops a theory appropriate for predicting the acoustically-drivendynamics of a single spherical gas bubble embedded in an incompressible lossyelastic solid. Use of this theory to calculate propagation parameters requirescalculation of the gas pressure component of section 2, and the options are outlined insection 3. The incorporation of radiation losses is discussed in section 4. Section 5discusses how the entire scheme can be incorporated into a nonlinear, time-dependentpropagation model

The use of acoustics in space exploration

In recent years increased attention has been paid to the potential uses of acoustics forextraterrestrial exploration. The extent to which acoustics per se is used in these studiesvaries greatly. First, there are the cases in which acoustics is simply the medium throughwhich some other time-varying non-acoustic signal (such as the output of a cosmic raydetector) is communicated to humans. Second, perturbations in a non-acoustic signal (e.g.EM) are interpreted through mechanisms relating to acoustic perturbations in the sourcematerial itself. Third, some probes have made direct measurements of acoustic signalswhich have been generated by the probe itself, as is done for example to infer the localatmospheric sound speed from the time-of-flight of an acoustic pulses over a shortdistance (O(10 cm)). Fourth, some studies have discussed ways of interpreting thenatural acoustic signals generated by the extraterrestrial environment itself. The reportdiscusses these cases and the limitations, implications and opportunities forextraterrestrial exploration using acoustics

Theory for acoustic propagation in solid containing gas bubbles, with applications to marine sediment and tissue

Whilst there is a considerable body of work in the literature on the theory of acoustic propagation in marine sediment, the incorporation of gas bubbles into such theories is done with the inclusion of assumptions which severely limit the applicability of those models to practical gas-laden marine sediments.Following an Introduction (section 1), section 2 develops a theory appropriate for predicting the acoustically-driven dynamics of a single spherical gas bubble embedded in an incompressible lossy elastic solid. Use of this theory to calculate propagation parameters requires calculation of the gas pressure component of section 2, and the options are outlined in section 3, with the implications for the description of dissipation. This leads to a discussion in section 4 into further of how dissipation enters the description, and in section 5 how the entire scheme can be incorporated into a propagation model

Derivation of the Rayleigh-Plesset equation in terms of volume

The most common nonlinear equations of motion for the pulsation of a spherical gas bubble in an infinite body of liquid arise in the various forms of the Rayleigh-Plesset equation, expressed in terms of the dependency of the bubble radius on the conditions pertaining in the gas and liquid. However over the past few decades several important analyses have begun with a heuristically-derived form of the Rayleigh-Plesset equation which considers the bubble volume, instead of the radius, as the parameter of interest, and for which the dissipation term is not derived from first principles. The predictions of these two sets of equations can differ in important ways, largely through differences between the methods chosen to incorporate damping. As a result this report derives the Rayleigh-Plesset equation in terms of the bubble volume from first principles in such a way that it has the same physics for dissipation (viscous shear) as is used in the radius fram

A method for estimating sound speed and the void fraction of bubbles from sub-bottom sonar images of gassy seabeds

There is increasing interest in the effect of bubbles in gassy sediment. This is, first, because ofthe impact those bubbles have on the structural integrity and load-bearing capabilities of thesediment; second, because the presence of bubbles can be indicative of a range of biological,chemical or geophysical processes (such as the climatologically-important flux of methanefrom the seabed to the atmosphere); and third, because of the effect which the bubbles haveon any acoustic systems used to characterise the sediment. For this reason, a range of methodshave been investigated for their ability to estimate the bubble population in the seabed. Withinsuch a range, there will a mix of advantages and limitation to given techniques. This reportoutlines a very basic method by which an observations which have already been taken forother purposes (sub-bottom profiles) may be subjected to a rapid analysis to obtain anestimate of the effect of bubbles on the sound speed in the sediment, and from there toprovide a rapid preliminary estimate of the void fraction of bubbles present (assuming quasistaticbubble dynamics). This approach is not meant to compete with large-scale field trialswhich deploy specialist equipment to monitor gas bubbles in sediment, but rather to provide amethod to exploit archived sub-bottom profiles, or to survey a large area rapidly withcommercial equipment from a small vessel, in order to obtain an estimation of the local voidfractions present, and their location and extent in three dimensions

Paying for Language Services in Medicare: Preliminary Options and Recommendations

Discusses how the federal government could design payment systems for language services in Medicare, and offers preliminary recommendations for implementing such programs

Prioritizing Urinary Incontinence for Current and Future Healthcare Professionals

Introduction: •Urinary incontinence (UI) is a common syndrome that often goes unreported and undiagnosed •As calls to action from the National Institute on Aging and American Geriatrics Society suggest, the healthcare workforce must work interprofessionally to meet the needs of people with UI •Understanding the challenges of and opportunities for improving continence care in Virginia is a first step •The primary goal of this study was to assess changes in awareness of and confidence in providing interprofessional UI care after participating in an interactive worksho