Biomedical subjects

J H Page

Publications and source records attributed to J H Page.

6 recordsLinked to original sources

PubMed2003

Field fluctuation spectroscopy in a reverberant cavity with moving scatterers.

We report a study of transient ultrasonic waves inside a reverberant cavity containing moving scatterers. We show that the elastic mean free path and the dynamics of the scatterers govern the evolution of the autocorrelation of acoustic wave field. A parallel is established between these results and a closely related technique, diffusing acoustic wave spectroscopy. Excellent agreement is found between experiment and theory for a moving stainless steel ball in a water tank, thereby elucidating the underlying physics, and a potential application, fish monitoring inside aquariums, is demonstrated.

Journal Article↗

PubMed2002

Diffusing acoustic wave spectroscopy.

We have developed a technique in ultrasonic correlation spectroscopy called diffusing acoustic wave spectroscopy (DAWS). In this technique, the motion of the scatterers (e.g., particles or inclusions) is determined from the temporal fluctuations of multiply scattered sound. In DAWS, the propagation of multiply scattered sound is described using the diffusion approximation, which allows the autocorrelation function of the temporal field fluctuations to be related to the dynamics of the multiply scattering medium. The expressions relating the temporal field autocorrelation function to the motion of the scatterers are derived, focusing on the types of correlated motions that are most likely to be encountered in acoustic measurements. The power of this technique is illustrated with ultrasonic data on fluidized suspensions of particles, where DAWS provides a sensitive measure of the local relative velocity and strain rate of the suspended particles over a wide range of time and length scales. In addition, when combined with the measurements of the rms velocity of the particles using dynamic sound scattering, we show that DAWS can be used to determine the spatial extent of the correlations in the particle velocities, thus indirectly measuring the particle velocity correlation function. Potential applications of diffusing acoustic wave spectroscopy are quite far reaching, ranging from the ultrasonic nondestructive evaluation of the dynamics of inhomogeneous materials to geophysical studies of mesoscopic phenomena in seismology.

Journal Article↗

PubMed2002

Ultrasound tunneling through 3D phononic crystals.

We report the study of ultrasound tunneling in 3D phononic crystals, consisting of fcc arrays of close-packed tungsten carbide beads in water. The transmission coefficient, phase velocity, and group velocity were measured along the [111] direction, allowing us to systematically investigate the tunneling of ultrasound at frequencies in the lowest band gap. Our experimental data are interpreted using multiple scattering theory, which provides a good explanation of our results. The effect of absorption and the difference between the tunneling of classical waves and quantum waves are discussed.

Journal Article↗

PubMed1999

Wave transport in random media: the ballistic to diffusive transition.

The character of wave transport through a strongly scattering medium, excited by a pulsed plane-wave source, is investigated as a function of sample thickness over the range from about one to 13 mean free paths. To examine the behavior theoretically, we perform a first-principles calculation of both the frequency correlation function of the transmitted field and the time-domain profile of the transmitted intensity. These quantities are investigated experimentally using an ultrasonic technique, which allows us to separate the ballistic and scattered components of the total transmitted field, and hence to measure the scattered component unambiguously in thin samples. For sample thicknesses greater than about four mean free paths, we find good agreement between our theory, the diffusion approximation, and our experimental data for both the frequency correlation function and the intensity time profile. In thinner samples, there are systematic differences between theory and experiment. To characterize the transition from ballistic to diffusive behavior in thin samples, we focus on the arrival time of the peak in the scattered component of the transmitted intensity; unexpectedly we find that the scattered peak arrival time exhibits an abrupt crossover between ballistic and diffusive behavior when the ratio of sample thickness to mean free path, L/l, is approximately equal to 3. Excellent agreement is obtained between our theory and experiment for this crossover behavior over the entire range of sample thicknesses investigated.

Journal Article↗

PubMed1996

Effect of wetting the mouth on aortic blood pressure just before taking sublingual nitrates.

The absorption of sublingual nitrate tablets is sometimes variable. We performed a randomized controlled trial to determine whether wetting the mouth improved the decrease in aortic systolic blood pressure (BP) from sublingual nitrate tablet or spray. The 100 patients undergoing routine diagnostic cardiac catheterization were allocated to control (no nitrate), 0.3 mg sublingual nitrate tablet, 0.4 mg sublingual nitrate spray, water + 0.3 mg sublingual nitrate tablet, or water + 0.4 mg sublingual nitrate spray. Aortic systolic and diastolic BP were recorded using a fluid-filled catheter and measured off-line blind to the treatment group. Compared with control subjects, there were significant decreases in aortic systolic BP with both nitrate preparations (tablet = -7.1 mm Hg, 95% confidence interval [CI] = -12.5 to -1.6 mm Hg; spray = -8.0 mm Hg, 95% CI = -13.4 to -2.5 mm Hg). On average, water significantly increased the fall in aortic systolic BP with nitrate tablets (-5.5 mm Hg, 95% CI = -10.9 to -0.1 mm Hg, p = 0.044) but did not significantly enhance the effect of nitrate spray (-2.8 mm Hg, 95% CI = -8.3 to 2.6 mm Hg). Water significantly increased the fall in aortic diastolic BP with tablets only (-2.9 mm Hg, 95% CI = -5.5 to -0.2), and had no significant effect on heart rate. Water had a consistently larger influence on the hemodynamic effects of nitrate tablets than on the effects of nitrate spray. Patients with a dry mouth will have an increased effect from sublingual nitrate tablets if they wet their mouth before using sublingual nitrate tablets. Water does not appear to assist in the action of sublingual spray.

Absorption↗

PubMed1996

Changes in job aspirations during physician training in Australia.

BACKGROUND: There is uncertainty regarding the effects of physician training on planned practice features of Australian physician trainees, for example plans for urban or rural, full-time or part-time and academic/research or purely clinical practice. These plans may differ between male and female trainees and between generalists and sub-specialists. AIM: To examine the changes in anticipated practice patterns over the course of advanced physician training. METHODS: Longitudinal study of doctors in Australia who passed the Part I clinical examination of the Royal Australasian College of Physicians in 1991, 1992 and 1993, followed annually up until 1995. Changes in future practice plans regarding full- or part-time work, rural or urban practice and pure clinical work or a mixture with research were examined among generalist and specialist trainees and among men and women. Statistical analysis included the calculation of chi square for trend statistics and intraclass correlation coefficients. RESULTS: At least one follow-up questionnaire was received form 80% of the 334 original respondents. The majority had been able to obtain their training job of choice. By the time of last follow-up, around 80% planned to practise in a capital city, indicating a shift during training from those who initially stated no preference. There was also a shift towards combining research with clinical practice and among women wishing to practise part-time only. Generalists were more likely to wish to practise outside a capital city than specialists. CONCLUSIONS: The training programme should be revised so that careers in rural and provincial centres are encouraged and so that it is sensitive to the needs for physicians to develop research capacity. Training and career opportunities should allow all candidates (particularly women) wishing part-time employment to achieve their full career potential.

Adult↗