Two blueschist belts in the North Qilian Mountains occur in Middle Cambrian and Lower Ordovician strata and strike N30-35"W for about 500 km along the Caledonian fold belt on the south-west margin of the SineKorean plate. The styles of metamorphism and deformation are quite different in the two belts. The Middle Cambrian to Ordovician rocks in the high-grade belt are mainly blueschists and C-type eclogites in which six phases of lower and upper crustal deformation have been recognized. The rocks contain glaucophane, phengite, epidote, clinozoisite, chlorite, garnet, stilpnomelane, piedmontite, albite, titanite and quartz. The estimated P-T conditions of eclogites are 340 f 10" C, 8 f 1 kbar and, of blueschist, >380" C, 6-7 kbar. The Ordovician rocks in the low-grade belt are characterized by ductile to brittle deformation in the middle to upper crust. The low-grade blueschists contain glaucophane, lawsonite, pumpellyite, aragonite, albite and chlorite. The estimated P-T conditions are 150-250" C and 4-1 kbar.K-Ar and " A T /~' A~ geochronology on glaucophane and phengite from the high-grade blueschist belt suggest two stages of metamorphism at 460-440 and 400-380Ma, which may represent the times of subduction and orogeny. The subduction metamorphism of the northern low-grade blueschist belt took place approximately at the end of the Ordovician.
In this paper,we describe a new design of semi-active laser guided decoding system based on FPGA.The system is designed to receive the echo pulse through a 4-qundrant laser sensor and process the digital laser pulses through analogdigital conversion,which are some fixed interval encoding signal reflected from the target.The decoding system improve the adjustment accuracy of the laser seeker,which reach 0.1us about 50 times in theory compared to current technology. State machine is used to address complicated laser signal,including how to hand of the identification and trapping of the correct laser pulses,how to hand of a state of anti-jamming,how to hand of capturing the laser pulses again after signal missing.And a real-time gate signal is adopted to enhance the ability of anti-interference [1] . Processed signal is used to monitor and control,the processed result is transmitted to a electric actuator and subsequently be sent to laser seeker as a guidance signal or to a PC to simulate and monitor or to be stored in Flash that can extract whenever needed. The whole performance of the system is oprated in laboratory and decoding model is simulated with Modelsim module in detail.The testing results show that the design can reduce the span of decoding time effectively,identify and track the echo pulses from target correctly even to the missed codes or interferential codes.The feasible technique wins the time for laser guidance,and has some theoretical and military value.
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