Neutron diffraction studies have been carried out on a single crystal of oxygen-deficient perovskite TbBaCo2O5.5 in the temperature range of 7-370 K. There have been observed several magnetic or structural transitions. Among these, the existence of the transitions to the insulating phase from the metallic one at ~340 K, to the one with the ferromagnetic moment at ~280 K and possibly to the antiferromagnetic one at ~260 K, with decreasing temperature T correspond to those reported in former works. We have studied the magnetic structures at 270 K and 250 K and found that all Co3+ ions of the CoO6 octahedra are in the low spin state and those of the CoO5 pyramids carry spins which are possibly in the intermediate spin state. Non-collinear magnetic structures are proposed at these temperatures. Two other transitions have also been observed at the temperatures, ~100 K and ~250 K.Comment: 9 pages, 2 tables, 10 figure

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The non-destructive evaluation technique using a piezoceramic (PZT) as an actuator-sensor has a potential to efficiently detect structural damage. In this technique, a PZT actuator-sensor patch is bonded on a structure. Through the measurement of its electrical impedance, which is related to the mechanical impedance of the structure being bonded, the change in structural properties due to damage can be detected. This paper presents the use of a PZT actuator-sensor in conjunction with numerical model-based methodology in structural health monitoring to quantitatively detect damage of bolted joints. The structure used in this study consists of two aluminium beams connected by a bolted joint. The damage was simulated by loosening the bolts. To quantitatively monitor the damage, a numerical model of the structure was formulated. A spectral element method (SEM), based on a wave propagation approach, was used to model the structure. A bonded-PZT beam and a bolted joint element were developed by using the SEM. The equations of motion were derived by using Hamilton's principle and then the spectral element matrices were formulated. Experimental results show the effectiveness of this method to detect the damage. By using the proposed model, the loosening of bolts can be quantitatively identified as the change in stiffness and damping at the bolted joint, indicating a high potential of this method in order to quantitatively monitor structural damage.

A new method of the microprocessor control of three phase sinusoidal voltage pulsewidth modulated (PWM) inverters is proposed. First, the discretized state equations of the inverter main circuit on the d-q frame have been derived. An algorithm of the dead beat control with a current minor loop that constrains the inverter current within the safety limit, is subsequently developed. To compensate the computing time delay, the second order prediction method, and a new discretization method using twice time of the sampling period have been adopted. This method is especially suitable for inverters using high speed switching devices and digital signal processors.

Transport and magnetic measurements have been carried out on perovskite Co-oxides R 1-x A x CoO 3 (R=La, Pr, and Nd; A=Ba, Sr and Ca; 0≤x≤0.5: All sets of the R and A species except No indication of this kind of transition has been observed in other species of R.