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[en] A theoretical simulation of electromagnetic and thermal fields was performed for a cryocooled superconducting bulk disc after applying a magnetic pulse. The results of the simulation qualitatively reproduced the experimental ones for the time and applied field dependences of the trapped field Bz and the temperature T on the bulk surface. For magnetic pulse application with a rise time of τ = 0.01 s, the magnetic flux propagation was about two orders of magnitude faster than the heat propagation because of the low thermal conductivity of the bulk. The results show that the intruding magnetic flux escaped because of the delayed temperature rise. For a longer magnetic pulse application with τ = 1 or 10 s, the flux propagation speed becomes slow and approaches the heat propagation speed. In this case, the magnetic flux escape attributable to the flux creep becomes small and a higher trapped field can be achieved. The method of exploring the enhancement of the trapped field using pulsed field magnetization is discussed.
[en] In this work, a typical pin-to-pin plasma synthetic jet in static air is excited by a pulsed DC power supply. The influences of the pulse rising time, the amplitude and the repetition frequency of the pulse voltage on the jet flow have been investigated. First, using a high-speed Schlieren imaging technique, the induced shock waves and the fast jet flow generated by the plasma synthetic jet are characterized. With a deposited energy of 44 mJ per pulse, the velocity of the shock wave and the maximum velocity of the jet flow reach 320 m s−1 and 100 m s−1, respectively. Second, when the applied voltage increases from 12.8 kV to 16 kV, the maximum jet velocity increases from 66 m s−1 to 93 m s−1. On the other hand, as the pulse rising time varies from 50 ns to 500 ns, or the pulse repetition frequency increases from 5 Hz to 40 Hz, the jet velocity induced by the plasma synthetic jet is weakly dependent. In addition, a comparative study of the plasma synthetic jets using three commercial pulsed power supplies (XJ-15, NPG-18, and PG-30) is implemented. It reveals that the maximum jet velocity of 120 m s−1 is obtained in the case of PG-30, with the longest pulse rising time and the lowest breakdown voltage, while the maximum velocity of 33 m s−1 is detected in the case of NPG-18, even though it has the shortest pulse rising time and the highest breakdown voltage. (paper)
[en] A modification of Smith predictor for controlling the higher order processes with integral action ad long dead-time is proposed in this paper. The controller used in this Smith predictor is an Integral-Proportional Derivative controller, where the Integrator is in the forward path and the Proportional and Derivative control are in the feedback, acting on the feedback signal. The main objective of this paper is to design a Dead Time Compensator(DTC), which has minimum tuning parameters, simple controller tuning, robust performance of tuning formulae and to obtain a critically damped system which is as fast as possible in its setpoint and load disturbance rejection performance. The controller in this paper is tuned by an adaptive method. This paper also presents a survey of various dead time compensators and their performance analysis
[en] Dead time effects can distort the shape of a time distribution curve. A method to measure events which are lost due to conversion and storing time is described. The variable conversion time for converters which only register one time interval per start pulse can be taken into account. The losses are measured separately. By correcting a time measurement a higher counting rate can be accepted, compared to an uncorrected measurement with the same systematic error. The method is simple to use and makes it easy to determine a suitable counting rate at the beginning of an experiment. An instrument for correction of time measurements applying this method is described and results from test measurements are given. (Auth.)
[en] The use of a data buffer enables the distribution of the time intervals between events to be studied for times less than the recording system dead-time but the usual negative exponential distribution for random events has to be modified. The theory for this effect is developed for an n-stage buffer followed by an asynchronous recorder. Results are evaluated for the values of n from 1 to 5. In the language of queueing theory the system studied is of type M/D/1/n+1, i.e. with constant service time and a finite number of places. (Auth.)