Acoustic CT System for Temperature Distribution and Wind Velocity Vector Measurement
In this report, a measurement method for cross-sectional temperature and wind velocity distribution is discussed. A novel method based on an acoustic CT technique is proposed. Specifically, the temperature and the wind velocity distributions are estimated simultaneously using the time of flight data of several ultrasonic propagation paths. The temperature and the wind velocity effects can be distinguished by considering sum and difference of the time of flight (TOF) data. Two types of projection data, temperature-oriented data and wind-velocity-oriented data, components are obtained. A filtered back projection method and inverse matrix method are applied to reconstruct the temperature and the wind velocity distributions, respectively. An experimental system is designed and fabricated to realize simultaneous temperature and wind velocity distribution measurements. Through this system, the effectiveness of the proposed measurement method is confirmed.
Primary study of temperature distribution measurement in stored grain based on acoustic tomography
Abstract A common and traditional method for detecting stored grain deterioration is the measurement of grain temperature. This study proposes a temperature monitoring method for stored grain based on acoustic tomography. A model describing the relationship between grain temperature and sound travel time in stored grain is established. A speed conversion coefficient is defined and used to convert the measured velocity of sound in the stored grain into the sound velocity in free space, which has the same gas components and temperature as those of the stored grain. The influence factors of the speed conversion coefficient are analyzed, and the calibration method of the coefficient is introduced. The time-delay estimation method based on triple correlation and wavelet de-noising and the temperature reconstruction algorithm based on Markov radial basis function and singular value decomposition are used to measure the temperature distribution of the grain bulk. Two experimental systems are built to verify the acoustic model and reconstruct the temperature distribution of grain. The experimental result shows that the acoustic model can be used for temperature measurement in soybeans. The temperature distributions with different hot spot locations in soybeans are all well reconstructed, and the coordinates of the hot spots are reconstructed with better accuracy than that in thermocouple measurement. Thus, acoustic temperature measurement is useful in the early prediction of temperature anomalies in stored grain.
Photoinduced spin-state transition of Co3+ in the layered perovskite manganite thin film
The photoinduced effect, at different temperatures, on layered perovskite manganite La1.2Sr1.8Mn1.8Co0.2O7 thin film deposited on a SrTiO3(100) substrate has been studied using a He–Ne laser (632.8 nm) with the power of output 25 mW at low temperatures. The electrical transport and magnetic properties of the film are investigated systematically in the temperature region from 20 to 300 K. The resistance shows a significant decrease at low temperatures (T<90 K) under laser irradiation, which can be interpreted in terms of the spin-state transition of Co3+ ions. The magnetic field combined with the laser is also used to detect the photoinduced effect of the spin-glass state. The time dependence of the metastable system under several applied fields was also discussed. The system has the ability to keep a persistent memory of the magnetic history imprinted in its zero-field resistance.