TAO, Vol. 16, No. 3, August 2005 622 Mainly medium to coarse-grained sands have accumulated on the Changyun Ridge to form sand banks. At the northern outlet of the Penghu Channel, the shoaling topography of the Changyun Ridge has caused a decrease in tidal current velocity and the subsequent deposition of sands, forming the present Changyun sand ridge. The formation of the eastern and western Changyun sand ridges is probably affected mostly by the tidal current patterns in the areas north of the Penghu Channel.

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We propose a new Polygonal Field Programmable Gate Array (PFPGA) that consists of many logic blocks interconnected by a generic three-stage three-sided rearrangeable polygonal switching network (PSN). The main component of this PSN consists of a polygonal switch block interconnected by crossbars. In comparing our PSN with a three-stage three-sided clique-based (Xilinx 4000-like FPGAs) (Palczewski; 1992) switching network of the same size and with the same number of switches, we find that the three-stage three-sided clique-based switching network is not rearrangeable. Also, the effects of the rearrangeable structure and the number of terminals on the network switch-efficiency are explored and a proper set of parameters is determined to minimize the number of switches. Moreover, we explore the effect of the PSN structure and granularity of cluster logic blocks on the switch efficiency of PFPGA. Experiments on benchmark circuits show that switches and speed performance are significantly improved. Based on experiment results, we can determine the parameters of PFPGA for the VLSI implementation.