No abstract

Emission of various hazardous air pollutants (HAPs) and greenhouse gases including perfluorocompounds (PFCs) from semiconductor industries, which individually may cause great impact on human health and the global environment, has attracted much public attention. In this paper, a potential application of nonthermal plasma technologies as an integrated approach for abating the emission of these gaseous pollutants is critically reviewed. Relevant studies indicate that direct electron impact with PFC molecules to form PFC fragment radicals is the first step leading to the destruction of PFCs in nonthermal plasmas (NTPs) and that further reactions of PFC fragments with radicals are essential for the effective removal of PFCs. Previous studies demonstrate that nonthermal plasma combined with catalyst or adsorbent has a good potential to be used as an integrated technology for abating PFCs from complicated gas streams of semiconductor manufacturing processes.

Ab~~ract-~ightning strikes tQ the 553-111 high CN Tower have been observed since 1978. Video records of CN Tower lightning events during the intervening lightning seasons, up to and including 1995, have been analyzed and statistical findings are presented, The paper includes data on monthly and diurnal occurrences of lightning, as well as on parameters of incidence; such as flash duration, multiplicity of strokes in a flash and interstroke intervals. Lightning data for CN Tower strikes are also compared with e elsewhere in the world. Information derived is relevant to lightning protection of tail structures and of neighbouring objects, and of power line and substation components, in particular those erected in mountainous regions.

[1] In this paper, analytical expressions relating far fields and currents associated with lightning strikes to tall towers are derived. The derived equations are general and can be used with any engineering model. It is shown that the far field can be decomposed into three terms, namely (1) contribution of the main return stroke pulse along the lightning channel, (2) contribution of the multiple-reflection process along the elevated strike object, including the contribution of upward propagating pulses transmitted into the channel, and (3) contribution of the so-called ''turn-on'' terms, associated with the current discontinuity at the return stroke wavefront. This discontinuity is associated with neglecting reflections at the upward moving front. It is also shown that only the first term is model-dependent and that the far field-current relationship does not significantly depend on the adopted engineering model. It is therefore possible to use the analytical equation relating the current peak and the associated distant electric or magnetic fields, derived by Bermudez et al. (2005) for the transmission line (TL) model, for any engineering model extended to include a tall strike object. It is also shown that the peak amplitude of the electromagnetic field radiated by a lightning strike to a tall structure is relatively insensitive both to the value of the return stroke speed and the top reflection coefficient. These results and findings of this paper emphasize the key differences between return strokes initiated at ground level (or from short strike objects) and those striking tall towers: (1) The electromagnetic field from lightning strikes to tall towers is largely determined by the tower and only to a lesser extent by the channel, (2) electromagnetic fields associated with tall strike objects are less model-sensitive than those corresponding to a strike to ground; in particular, the early time response of the field is nearly model-independent, and (3) unlike ground-initiated strikes, for which the far field peak is strongly dependent on the return stroke speed (proportional according to the TL model), far field peaks associated with strikes to tall strike objects are little sensitive to the return stroke speed. This is a particularly interesting result when lightning currents are measured directly on instrumented towers to calibrate the performance of lightning location systems, since in most practical cases the value of the return stroke speed is unknown. Note that points (2) and (3) can be considered as corollaries of point (1).

No abstract

No abstract

Using an eight‐channel photodiode system, we resolved in time and space the luminous propagation of lightning attachment to the CN tower. Approximately 60 lightning discharges were recorded during 1991 and 1992. Most of these discharges demonstrated simultaneous, bidirectional propagation starting at several tens of meters above the top of the CN tower. Propagation speeds ranged from 8×10° to 287×106 m/s. The observed bidirectional propagation suggests the presence of space leaders or the reilluminations following these space leaders during the initial stage of development of upward leaders from the CN tower. A few of the bidirectional discharges were found to have the return stroke speeds and these might be deduced to be manifestations of the bidirectional propagation processes of return strokes which occurred after the connection of a downward leader and an upward connection leader. We also recorded portions of seven ordinary dart leader—return stroke sequences. The dart leader speeds ranged from 7×106 to 23×106 m/s; the velocities of the return strokes ranged from 88×106 to 143×106 m/s. These values are in excellent agreement with the previous results by other authors. Positive correlations are found among the return stroke velocity, the leader velocity, and the leader light intensity. However, it also is observed that even in the case of a very tall structure, when a dart leader approaches the CN tower, it is highly possible that no apparent connecting leader is initiated before the ensuing return stroke.

No abstract