Transducers in medical ultrasound. Part 4: Transducer safety

Transducer safety encompasses a wide spectrum of topics. It may range from mechanical construction reliability to biological effects created by ultrasound radiation. In this Paper the electrical and acoustical safety aspects are summarized and initial experience with sterilization of echocardiographic transducers for peroperative cardiac scanning is mentioned.     

Coherent single pion production by antineutrino charged current interactions and test of PCAC

The cross section for coherent production of a single π^? meson in charged current antineutrino interactions on neon nuclei has been measured in BEBC to be (175±25) 10^?40 cm²/neon nucleus, averaged over the energy spectrum of the antineutrino wide band beam at the CERN SPS; this corresponds to (0.9±0.1) % of the total charged current \(\bar v_\mu \) cross section. The distributions of kinematical variables are in agreement with theoretical predictions based on the PCAC hypothesis and the meson dominance model; in particular, theQ ² dependence is well described by a propagator containing a massm=(1.35±0.18) GeV. The absolute value of the cross section is also in agreement with the model. This analysis thus provides a test of the PCAC hypothesis in the antineutrino energy range 5–150 GeV.     

Inclusive ϕ production inK − p interactions at 110 GeV/c and search for structure in φ π−

Results on inclusive ? production inK ^? p interactions at 110 GeV/c are presented. The production cross section is found to be larger than in πp andpp interactions at similar energies, suggesting OZI allowed \(s\bar s\) fusion to be the dominant mechanism in ? production. Thex distributions of ? and \(\bar K^{*0} \) are found to be similar to each other over the entirex range suggesting an overall strangeness suppression factor of 0.20±0.04 in the sea to be the dominant source of the difference in the cross section for ? and \(\bar K^{*0} \) . There is no evidence of a narrowφπ ^? state around 2.1 GeV/c² as suggested byK ⁺ experiments, but there is some excess of events in the region 1.94?1.98 GeV/c² consistent with theF-meson mass as observed ine ⁺ e ^? experiments.     

Classification of generic 3-dimensional Lagrangian singularities with (Z2) l -symmetries

The paper provides the complete list of local models forZ ₂ ^l -invariant generic germs of Lagrangian submanifolds of dimension ≦3. Classification is done directly for genrating functions of Lagrangian submanifolds and contains both elementary singularities and non-elementary ones with continuous moduli. The results demonstrate, in particular, that in contrast to the non-equivariant case the classification of equivariant Lagrangian singularities is not subordinated to the classification of symmetric functions up to the right equivariant equivalences.     

Search for exclusive multibody non- decays at the resonance

Using data collected at the psi(3770) resonance with the CLEO-c detector at the Cornell e+e- storage ring, we present searches for 25 charmless decay modes of the psi(3770), mostly multibody final states. No evidence for charmless decays is found.     

Negative thermal expansion in ZrW2O8: mechanisms, rigid unit modes, and neutron total scattering

The local structure of the low-temperature ordered phase of the negative thermal expansion (NTE) material has been investigated by reverse Monte Carlo (RMC) modeling of neutron total scattering data. We obtain, for the first time, quantitative measurements of the extent to which the and polyhedra move as rigid units, and we show that these values are consistent with the predictions of rigid unit mode theory. We suggest that rigid unit modes are associated with the NTE. Our results do not support a recent interpretation of x-ray-absorption fine structure spectroscopy data in terms of a larger rigid structural component involving the Zr-O-W linkage.     

Direct measurement of fluid velocity gradients at a wall by PIV image processing with stereo reconstruction

Velocity gradient is typically estimated in Particle Image Velocimetry (PIV) by differentiating a measured velocity field, which amplifies noise in the measured velocities. If gradients near a boundary are sought, such noise is usually greater than in bulk fluid, because of small tracer displacement, uncertainty in the effective positions of velocity vectors, intense deformation of tracer patterns, and laser reflection. We consider here a modified form of the Particle Image Distortion (PID) method todirectly calculate velocity gradients at a fixed wall, and refer it as “PIV/IG” (“Interface Gradiometry”). Results from synthetic 2D PIV images suggest our method achieves higher SNR and accuracy than velocity differentiation. Also, we have developed a procedure to reconstruct three-dimensional velocity gradient at a fixed wall the two non-zero components from PIV/IG data obtained in stereo views; these equations simplify considerably thanks to the no-slip condition. Experimental data from the bottom wall of turbulent open channel flow appear to suffer from a form of pixel locking. As with standard PIV, this underlines the importance of adequate tracer diameter in the images, sufficient seeding density, and of dynamic range of the camera sensor.     

Transient development of backward stimulated Raman and Brillouin scattering on a picosecond time scale measured by subpicosecond thomson diagnostic

The excitation and the relaxation of the plasma waves and ion acoustic waves (IAW), respectively, driven by stimulated Raman (SRS) and Brillouin (SBS) backscatterings have been experimentally investigated with short-pulse lasers. The spectra have been obtained with a 0.3 ps time resolution. It is shown that SRS develops before SBS and suddenly decays around the peak of the pump, as the IAW reaches saturation. On this short time scale, electron kinetic effects play a major role for SRS saturation, contrary to ion dynamics. These results are supported by particle-in-cell simulations.