Direct observation of soft mode stiffening in V3Si by high magnetic fields

The velocity of the soft associated with the martensitic phase transition in V₃Si has been studied by ultrasonic means in magnetic fields up to 84 kOe for temperatures between 10 and 25K. Above the superconducting transition temperature the velocity of this mode has been found to increase quadratically with field, in agreement with the lattice stiffening effect predicted by Dieterich and Fulde.     

Measurement of the acoustic nonlinearity parameter in 1-alkanols

We present a harmonic generation method based on a pitch-catch experimental setup and the calculation of the corresponding nonlinear parameter in 1-alkanols, from methanol to 1-decanol. By focusing a 14 MHz ultrasonic toneburst through a spherical quartz lens in these alcohols, a second harmonic is produced and measured as a function of distance by a 28 MHz piezoelectric transducer placed near the focus. By extracting the point where the second harmonic power is at a maximum in each liquid, the corresponding nonlinear parameter is then computed with a model developed by Germain et al. The preliminary results from this experiment are in reasonable agreement with the values found in the literature for primary alcohols and support the idea that the nonlinear parameter is dependent on the chain structure.     

Dependence of single-bubble sonoluminescence on ambient pressure

Kondic et al.'s theory makes several specific predictions on the dependence of single-bubble sonoluminescence (SBSL) on ambient pressure. We have carried out experiments to verify these predictions for air bubbles in a water-glycerine mixture at about 17.5 kHz. The results show an increase in SBSL with reduced ambient pressure down to a critical value below which SBSL is extinguished. The results are all in good agreement with Kondic et al.'s theory and are also compatible with the dissociation hypothesis of Lohse et al.     

Orientation dependence of the memory echo in piezoelectric powders

Observation of two pulse and memory echoes in TeO₂ powder is reported. An electric field rotation experiment on the reading pulse gives a cos²θ dependence of the echo amplitude. This is in apparent disagreement with the predictions of the orientation model.     

Acoustic phonons in the transition-metal dichalcogenide layer compound,TiSe2

The frequencies of acoustic phonons have been measured in the layer-type substance TiSe₂ by neutron inelastic scattering techniques. As expected from the two-dimensional nature of such substances the in-plane longitudinal sound velocity is much larger than that perpendicular to the layer, while the transverse mode propagating in the layer but polarised perpendicular to the layer exhibits an upwards curvature.     

高T_c超导体YBCO磁通钉扎的计算机模拟研究

临界电流密度Jc是影响高温超导体在强电领域应用的一个重要参数,在实际应用中,特别在外加磁场下,临界电流密度与超导材料的磁通钉扎性质密切相关.因此,磁通钉扎一直是高温超导体研究中的一个重要领域.由于高温超导体磁通钉扎力密度Fp的标度律存在,本文根据D.Dew-Hughes总结的钉扎力函数,主要存在两种主要作用类型(正常相和△K).我们将D.Dew-HugBes给出的钉扎力密度Fp标度函数改进为一个简化的具有物理意义的函数表达式.结合文献中已有的实验数据,我们对YBcO进行了计算机模拟,确定了它的磁通钉扎类型,模拟的研究结果与实际情况比较吻合.     

Hypersonic attenuation near Hc1 in superconducting niobium

Results are reported of hypersonic attenuation at 9 GHz near H_c1 in niobium. We observe a break in the variation of attenuation with applied magnetic field, associated with the existence of the intermediate mixed state.