Acoustic microscopy applied to nonlinear characterization of biological media

The use of an acoustic microscope as a method for nonlinear characterization of biological media is evaluated. The method consists of measuring the second harmonic signal generated in a sample located at the focus of the acoustic lens. Two experimental configurations were compared: The first is the simple case where the sample is a liquid mixture filling the space between the lens cavity and the receiver; in the second case, the liquid mixture is confined to a thin layer at the focal plane, in order to simulate a real tissue layer. Aqueous solutions of ethylene glycol and methanol were used as liquid samples. Simple theoretical models are presented for each configuration and the predictions show good qualitative agreement with experimental measurements. These results confirm our belief that the acoustic microscope is potentially a good tool for nonlinear B/A imaging of biological systems.     

Kapitza resistence of low acoustic impedance solids (ice and bismuth)

Results of the Kapitza resistance between ice and bismuth and superfluid helium in the 1–2K range are presented. Reasonable agreement with theory is obtauned, consistent with the comparatively good acoustic matching between these solids and liquid helium.     

Operator algebras and a theorem of Dieudonne

LetA be aC*-algebra with second dualA″. Let (φ _n)(n=1,...) be a sequence in the dual ofA such that limφ _n(a) exists for eacha εA. In general, this does not imply that limφ _n(x) exists for eachx εA″. But if limφ _n(p) exists whenever p is the range projection of a positive self-adjoint element of the unit ball ofA, then it is shown that limφ _n(x) does exist for eachx inA″. This is a non-commutative generalisation of a celebrated theorem of Dieudonné. A new proof of Dieudonné’s theorem, for positive measures, is given here. The proof of the main result makes use of Dieudonné’s original theorem.     

Radial oscillations of neutron stars in strong magnetic fields

The eigen frequencies of radial pulsations of neutron stars are calculated in a strong magnetic field. At low densities we use the magnetic BPS equation of state (EOS) similar to that obtained by Lai and Shapiro while at high densities the EOS obtained from the relativistic nuclear mean field theory is taken and extended to include strong magnetic field. It is found that magnetized neutron stars support higher maximum mass whereas the effect of magnetic field on radial stability for observed neutron star masses is minimal.     

Simulation of electromechanical coupling coefficient by modified modal frequency spectrum method including the electrode effect

An approximate formula has been developed to determine the electromechanical coupling coefficient of the piezoelectric film in a four-layer composite resonator, which includes two electrodes. In this formula, the coupling coefficient can be calculated from the distribution of the effective coupling coefficients, k2eff, which are given by the modal frequency spectrum of the composite resonator. The feasibility of this method has been demonstrated with a ZnO/SiO2 composite resonator for different electrode thickness. The effect of mechanical propagation loss in both piezoelectric layer and substrate has also been studied.     

Observation of magnetic field dependent ultrasonic relaxation time in p-InSb

Ultrasonic attenuation and sound velocity measurements are presented for p-InSb (≈ 10¹⁴cm^?3) at low temperatures in high magnetic fields. A magnetic field dependent relaxation time is observed, which is interpreted as being due to a relaxation process via holes in the valence band.