As a tradeoff of GEO and LEO, MEO satellite system has more acceptable service performance and it is more appropriate to provide global mobile communications. A MEO satellite system model communicating according to time slots is constructed in the paper. Moreover, in order to improve comprehensive performance of the network, a novel routing algorithm applying Time Evolving Graph based on Pairing Heap is proposed. The Time Evolving Graph is employed to analysis the dynamic topology of the network and the Pairing Heap is applied in the Dijkstra algorithm to reduce the time complexity. By contrast, Fibonacci Heap is also used to optimize Dijkstra algorithm. Finally simulation results show that routing algorithm applying Time Evolving Graph based on Pairing Heap can perform better and reduce the time complexity obviously, and at the same time, Pairing Heap works better than Fibonacci Heap when the number of nodes grows bigger.
TiC-based coating is prepared by depositing TiO 2 sol on cemented carbide compact and liquid phase sintering. TiC forms due to carbothermal reduction reaction of TiO 2 and then reacts with WC and transforms to TiC-based solid solution. Ti content changes the WC growth mechanism and results in the multi-stepped morphology. When sintered cemented carbide is used as substrate, WC keeps the equilibrium truncated triangle prism morphology due to the relatively weak diffusion among Ti, WC, and Co.TiC is extensively used as an intermediate layer or final coatings on cemented carbide tools or wear parts due to its high hardness, thermal stability, wear resistance, oxidation resistance, and low friction coefficient. [1] Vapor deposition methods are widely used in industrial scale to coat TiC on cemented carbide. [2][3][4] However, expensive furnaces are required and the controlling of processing parameters is complicated. Furthermore, CVD coatings are typically deposited at relatively high temperatures of 773 K~1323 K (500°C~1050°C), [5] which has neglect effect on the toughness and hardness of substrates and adhesion strength of coatings. [6] Sol-gel technique is a simple and inexpensive coating method, which has many advantages including low processing temperature, better control of coating composition, and ease of coating on substrates of complex geometries. [7] Sahnesarayi [8] synthesized the TiO 2 polymeric sol through partial hydrolysis and condensation of titanium isopropoxide as the starting material. The TiO 2 coatings were prepared on the stainless steel substrate via dip-coating at a withdrawal speed of 3 cm/min and heat treating at 673 K~973 K (400°C~700°C) for 30 minutes. Dong [9] synthesized anatase TiO 2 thin films on fused quartz by sol-gel dip-coating method followed by annealing at 800 K (527°C). Hu [10] prepared dense Al 2 O 3 precursor using aluminum isopropoxide (Al(OPri) 3 ) as raw material, and dense Al 2 O 3 thin film were obtained by spin-coating of the sol on fused Pt/Ti/SiO 2 /Si wafers and followed by drying at 473 K (200°C) for 10 minutes, pyrolyzing at 673 K (400°C) for 10 minutes, and calcining at 773 K (500°C) for 3 hours. Chen [11] prepared boehmite sol at 363 K(90°C) from aluminum isopropoxide solution by a sol-gel route. Al 2 O 3 film was fabricated after depositing the sol on cemented carbide and sintering at 1423 K to 1573 K (1150°Cto 1300°C). It should be noted that sol-gel method is typically characterized by hydrolysis and condensation of metal salt, followed by calcination, thus generally yielding an oxide other than carbide.In the paper, sol-gel method is utilized to prepare TiC-based coating. TiO 2 sol is prepared and deposited onto cemented carbide compact other than as-sintered bodies, and then TiC-based coating can be achieved due to the carbothermal reaction of TiO 2 during vacuum sintering of the TiO 2 sol-coated green body. Furthermore, neglect effect of coating process on the substrate can be avoided since the compact other than sintered cemented carbide is used as the sub...
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