A level measuring system has been investigated to work with the electromagnetic continuous casting of steel billet, based on the principle of electromagnetic induction. The basic idea of the development is the distinction of the magnetic field measured in the mold into the effect of the applied one and the effect of the level variation. Several candidates of induction type magnetic probes were devised and examined. It was seen that the so-called global sensor was the proper one from the viewpoint of sensing range, resolution of the signal, and robustness to the external perturbation. The level of the melt was successfully calculated from the sensor output by employing the reference voltage for the set current in the power supply as a measure of the applied magnetic field. The use of the global sensor associated with the electronic device and the program showed that the resolution of the measurement was within Ϯ0.2 mm, the dynamic range of sensing the level was 0-300 mm below the top of the mold under the electromagnetic field at 20 kHz. In its application to commercial scale electromagnetic continuous casting at a billet caster of POSCO works, it worked well with the existing control device in supplying the molten steel to the mold. Particularly, its accuracy and promptness was sufficient to control the level at the initial stage of casting.

The current–voltage (I–V) characteristics of carbon nanotubes (CNTs) during field emission were investigated by in situ imaging and field-emission (FE) measurement inside a field-emission scanning electron microscope (FE-SEM). A primary electron of the FE-SEM could induce and enhance a large stimulated electron emission from a CNT which might be due to the strong local field on the tip of the CNT in the presence of an applied voltage. FE of bent nanotubes (BNTs) can initially occur after they are fully straightened or it can start in the bent state (during geometrical straightening) as the applied field increases. The FE from a single CNT follows FN (Fowler–Nordheim) behaviour with a single linear slope in the FN plot. The FE from two nanotubes with a geometrical change during FE showed transition of the FN slope from the low voltage to the high voltage region, which could be due to interactions between two dynamic neighbouring BNTs.

No abstract

No abstract