The manufacture of a three-dimensional transducer used in laboratory

Since the development of ultrasonic pulse technique seismologists can study the seismic problems by simulation experiments in laboratries. In the 1950s Oliver (1954) conducted two-dimensional seismic model experimental study. Henceforth geophysical model experiments have been conducted widly all over the world. In 1958 Zhao et al. of Peking University built the apparatures for seismic model experiments and did various model experiments (Zhao, 1986). In the 1960s, Birch (1960) measured the velocity of seismic waves in rocks under high pressure and first used the ultrasonic technique in the measurement of physical properties of rocks under high pressure. Since the end of the 1960s people paid attention to wave velocity anomaly as a seismic precursor, and simulation experiments of wave velocity anomoly have been developed (Nur, 1969; Liu and Lai, 1986; Liu, 1989). In the 1980s the developments of three-dimensional AE loation technique provided the conditions for study of seismic source mechanism in the laboratory (Kusunose, et al., 1981 ). All the experimental studies mentioned above used one-dimensional transducers. But the experiments require three-dimensional transducers with high precision to get accurate experimental data. We have manufactured three-dimensional transducers used in the laboratory,and they are able to stand high temperature and high pressure. By using the three-dimensional transducer in the laboratory the shape and the arrival times of longitudinal wave (P) and transverse wave in two polarization directions (S1, S2) can be measured simulataneously. Therefore, in the measurement of parameters of physical properties, the velocities, attenuation properties and frequency spectra of longitudinal wave (P) and transverse waves (S1, S2) can be measured with the same sample in the same experiemnt. Thus the problem caused by the difference in conditions of two experiments can be avoided. These trnasducers can also be used in model experiments and acoustic-wave position location, and under high temperature and high pressure conditions.

Structural Characterization of Thin Epitaxial GaN Films on Polymer Polyimides Substrates by Ion Beam Assisted Deposition

The Epitaxial GaN thin films have been fabricated by Ion Beam Assisted Deposition (IBAD) process using nitrogen ions with hyperthermal energies on the polyimides polymer substrates. By applying with the Reflection of High-Energy Electron Diffraction (RHEED), Scanning Electron Microscopy (SEM) and Quantum Design Physical Properties Measurement System, the behaviour of hexagonal GaN thin films is investigated. The result showed that the high quality of the deposited GaN layers kept appearing for many parameters depending on the temperature greatly. The behaviour of high quality of epitaxial GaN coating on the polyimide polymer substrates is a promising material for optoelectronic devices and semiconductor devices application.

Low-temperature Heat Capacity and Standard Thermodynamic Functions of D-Galactose and Galactitol

The heat capacities of D-galactose and galactitol were measured on a quantum design physical property measurement system（PPMS） over a temperature range of 1.9-300 K, and the experimental data were fitted to a function of T using a series of theoretical and empirical models in appropriate temperature ranges. The fit results were used to calculate thermodynamic function values, C^θp,m, ^T0S0^θm , and △^T0H^θm from 0 K to 300 K. The standard molar heat capacity, entropy and enthalpy values of D-galactose and galactitol at 298.15 K and 0.1 MPa were determined to be C^θp,m=（227.96±2.28） and（239.50±2.40） J·K^-1·mol^-1, S0^θm = （211.22±2.11） and （230.82±2.30） J·K^-1·mol^-1 and μm = （33.95±0.34） and （36.57±0.37） kJ/mol, respectively.