Superconductivity and physical properties of Ba24Si100 determined from electric transport, specific-heat capacity, and magnetic susceptibility measurements

Both Ba24Si100 and Ba24Ge100 with crystallographically identical structure are found to be superconducting at 1.4 and 0.27 K, respectively. Physical properties of this superconductor Ba24Si100 are studied by electric transport, specific heat capacity, and magnetic susceptibility measurements. The density of states at the Fermi level NEF=0.148 states eV-1(Siatom)-1 and a distinct jump of Cp at the superconducting transition temperature ΔCp=0.272JK-1mol-1 are obtained. An exponential fit of Cp below the superconducting states gives an energy gap 2Δ=0.423meV and shows that this is a superconductor having s-wave character or isotropic energy gap. On the basis of our experimental data other important physical parameters are also derived

Measurement of elastic constant and refraction index of thin films at low temperatures using picosecond ultrasound

In this paper, a picosecond ultrasound measurement is conducted to evaluate the low-temperature elastic and optical properties of thin films and semiconductors. Specimens are cooled with liquid He through a heat exchanger in a cryostat, and an ultrahigh-frequency acoustic pulse is generated using a femtosecond light pulse, which propagates in the film-thickness direction. Pulse echoes of the longitudinal wave and Brillouin oscillation are observed by the changes in reflectivity of the time-delayed probe light, which depend on the material, and give the longitudinal-wave out-of-plane elastic constant. When the stiffness is known, the Brillouin oscillation provides the refractive index. We determined the stiffness of a Pt thin film and the refractive index of Si at 5 K. The methodology developed in this paper is useful for studing the elastic and optical properties of metallic thin films and transparent materials at cryogenic temperatures.Kenichi Tanigaki, Tatsuya Kusumoto, Hirotsugu Ogi, Nobutomo Nakamura and Masahiko Hirao. Measurement of elastic constant and refraction index of thin films at low temperatures using picosecond ultrasound. Japanese Journal of Applied Physics, 2010, 49(7S), 07HB01. https://doi.org/10.1143/JJAP.49.07HB01

Monitoring of longitudinal-wave velocity and attenuation of SrTiO 3 at low temperatures using picosecond ultrasound spectroscopy

Nagakubo A., Yamamoto A., Tanigaki K., et al. Monitoring of longitudinal-wave velocity and attenuation of SrTiO 3 at low temperatures using picosecond ultrasound spectroscopy. Japanese Journal of Applied Physics, 51(7) PART2, 07GA09 (2012) https://doi.org/10.1143/JJAP.51.07GA09

The compressive behaviour and constitutive equation of polyimide foam in wide strain rate and temperature

These days, polymer foams, such as polyurethane foam and polystyrene foam, are used in various situations as a thermal insulator or shock absorber. In general, however, their strength is insufficient in high temperature environments because of their low glass transition temperature. Polyimide is a polymer which has a higher glass transition temperature and high strength. Its mechanical properties do not vary greatly, even in low temperature environments. Therefore, polyimide foam is expected to be used in the aerospace industry. Thus, the constitutive equation of polyimide foam that can be applied across a wide range of strain rates and ambient temperature is very useful. In this study, a series of compression tests at various strain rates, from 10−3 to 103 s−1 were carried out in order to examine the effect of strain rate on the compressive properties of polyimide foam. The flow stress of polyimide foam increased rapidly at dynamic strain rates. The effect of ambient temperature on the properties of polyimide foam was also investigated at temperature from − 190 °C to 270°∘C. The flow stress decreased with increasing temperature

The compressive behaviour and constitutive equation of polyimide foam in wide strain rate and temperature

These days, polymer foams, such as polyurethane foam and polystyrene foam, are used in various situations as a thermal insulator or shock absorber. In general, however, their strength is insufficient in high temperature environments because of their low glass transition temperature. Polyimide is a polymer which has a higher glass transition temperature and high strength. Its mechanical properties do not vary greatly, even in low temperature environments. Therefore, polyimide foam is expected to be used in the aerospace industry. Thus, the constitutive equation of polyimide foam that can be applied across a wide range of strain rates and ambient temperature is very useful. In this study, a series of compression tests at various strain rates, from 10−3 to 103 s−1 were carried out in order to examine the effect of strain rate on the compressive properties of polyimide foam. The flow stress of polyimide foam increased rapidly at dynamic strain rates. The effect of ambient temperature on the properties of polyimide foam was also investigated at temperature from − 190 °C to 270°∘C. The flow stress decreased with increasing temperature

Observation of higher stiffness in nanopolycrystal diamond than monocrystal diamond

Tanigaki K., Ogi H., Sumiya H., et al. "Observation of higher stiffness in nanopolycrystal diamond than monocrystal diamond", Nature Communications, 4, 2343 (2013). https://doi.org/10.1038/ncomms3343

Simulation of dynamic response of projectile and granular target

In the present study, the three-dimensional elastic discrete element method (DEM) and the elastic finite element method (FEM) analysis were, respectively, applied to the randomly distributed identical spheres as a granular target and to the cylindrical projectiles in order to clarify dynamic response during penetration. In the target, it was found that highly densified region was formed just ahead of the projectile and began to propagate spherically at much higher velocity than that of projectile leaving relatively rarefied region. It was also found that the peak resistance during penetration was closely related to the initial formation of densified region and was expressed in terms of momentum change of target particles accelerated by the projectile. Stress wave propagation in the projectiles with various body lengths was investigated during penetration and was discussed in connection with dynamic response of target particles ahead of the projectile. Effect of mechanical properties of projectile on the peak resistance was also investigated and was understood in connection with dynamic behavior of target particles

Simulation of dynamic response of projectile and granular target

In the present study, the three-dimensional elastic discrete element method (DEM) and the elastic finite element method (FEM) analysis were, respectively, applied to the randomly distributed identical spheres as a granular target and to the cylindrical projectiles in order to clarify dynamic response during penetration. In the target, it was found that highly densified region was formed just ahead of the projectile and began to propagate spherically at much higher velocity than that of projectile leaving relatively rarefied region. It was also found that the peak resistance during penetration was closely related to the initial formation of densified region and was expressed in terms of momentum change of target particles accelerated by the projectile. Stress wave propagation in the projectiles with various body lengths was investigated during penetration and was discussed in connection with dynamic response of target particles ahead of the projectile. Effect of mechanical properties of projectile on the peak resistance was also investigated and was understood in connection with dynamic behavior of target particles

DEM/FEM simulation for impact response of binary granular target and projectile

Three-dimensional dynamic discrete element method (DEM) and finite element method (FEM) simulation using LS-DYNA were, respectively, applied to the randomly distributed binary granular material and to the cylindrical projectiles in order to clarify the effect of size distribution of target particles on the dynamic behaviour of low density granular material. It was found that the peak resistance force of projectile during penetration depends on the packing density of the granular materials and on the impact velocity of projectile. The change of resistance force was well understood in connection with the propagation and the reflection of stress wave in projectile. The variety of particle size almost did not affect the resistance force of projectile. Densified region in granular material was generated ahead of projectile after impact. The densified region propagated in the depth direction and its propagation speed depended on the packing density of target granular material and impact velocity of projectile. That is, projectile impact behaviours of granular materials can be uniformly handled by impact velocity and packing density of the granular material, not depending on the variety of the particle size

Numerical study on dynamic compressive deformation and elasto-plastic wave propagation of foam materials

Finite element models of closed-cell foam structures were created using the three-dimensional Voronoi tessellation method coupled with the random sequential addition algorithm. The dynamic compressive deformation behaviors of the models were numerically studied using LS-DYNA code. The deformation mode of the models changed gradually as the deformation rate increases. Also, the generation and the propagation of plastic wave was clearly observed with the rate of 100 m/s. The longitudinal elastic wave velocity showed a weak negative dependency on the deformation rate although the strain rate dependence of material properties was not considered. Furthermore, a prediction method for the dynamic stress state on the impact side based on the static stress-strain relationship was presented