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( Zhang Yankui ),( Xu Haiyun ),( Ba Bin ),( Zong Rong ),( Wang Daming ),( Li Xiangzhi ) 한국인터넷정보학회 2019 KSII Transactions on Internet and Information Syst Vol.13 No.5
The existing direct position determinations(DPD) for coherently distributed(CD) sources are mostly applicable for uniform linear array(ULA), which result in a low degree of freedom(DOF), and it is difficult for them to realize the effective positioning in underdetermined condition. In this paper, a novel DPD algorithm for coherently distributed sources based on compressed sensing with a moving nested array is present. In this algorithm, the nested array is introduced to DPD firstly, and a positioning model of signal moving station based on nested array is constructed. Owing to the features of coherently distributed sources, the cost function of compressed sensing is established based on vectorization. For the sake of convenience, unconstrained transformation and convex transformation of cost functions are carried out. Finally, the position coordinates of the distribution source signals are obtained according to the theory of optimization. At the same time, the complexity is analyzed, and the simulation results show that, in comparison with two-step positioning algorithms and subspace-based algorithms, the proposed algorithm effectively solves the positioning problem in underdetermined condition with the same physical element number.
Casting Defects of Ti-6Al-4V Alloy in Vertical Centrifugal Casting Processes with Graphite Molds
Limin Jia,Daming Xu,Min Li,Jingjie Guo,Hengzhi Fu 대한금속·재료학회 2012 METALS AND MATERIALS International Vol.18 No.1
Numerical simulation and experimental investigation are utilized to analyze the casting defects of Ti-6Al-4V alloy formed under different vertical centrifugal casting conditions in graphite molds. Mold rotating rates of 0, 110 and 210 rpm are considered in experimental process. Results show that centrifugal forces have significant effects on the quantity of both macropores and microdefects (micropores, microcracks and inclu-sions). The relative amount of all macro- and micro-scopic casting defects decreases from 62.4 % to 24.8 %with the increasing of the centrifugal force, and the macropore quantity in stepped casting decreases expo-nentially with the increase of the gravitation coefficient. The relative proportions of both micropores and microcracks decrease with the mold-rotating rate increase, but the relative proportion of inclusions increases significantly. Besides this, the mold-filling sequence is proved to be an important factor in casting quality control.
TRIGONOMETRIC PARALLAXES OF STAR FORMING REGIONS IN THE PERSEUS SPIRAL ARM
Choi, Y. K.,Hachisuka, K.,Reid, M. J.,Xu, Y.,Brunthaler, A.,Menten, K. M.,Dame, T. M. IOP Publishing 2014 The Astrophysical journal Vol.790 No.2
<P>We report trigonometric parallaxes and proper motions of water masers for 12 massive star forming regions in the Perseus spiral arm of the Milky Way as part of the Bar and Spiral Structure Legacy (BeSSel) Survey. Combining our results with 14 parallax measurements in the literature, we estimate a pitch angle of 9 degrees.9 +/- 1 degrees.5 for a section of the Perseus arm. The three-dimensional Galactic peculiar motions of these sources indicate that on average they are moving toward the Galactic center and slower than the Galactic rotation.</P>