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991.
To improve the performance of automatic optical inspection (AOI), a neural network combined with genetic algorithm for the diagnosis of solder joint defects on printed circuit boards (PCBs) assembled in surface mounting technology (SMT) is presented. Six types of solder joint have been classified in respect to the reality in the manufacture. The images of solder joint under test are acquired and 14 features are extracted as input features for the classification. The neural network is easily become over-fitting because these input features are not independent of each other, so the genetic algorithm is introduced to select and remove redundant input features. The experimental results have proved that the neural network combined with genetic algorithm reduced the number of input feature and had a satisfying recognition rate. 相似文献
992.
The electron paramagnetic resonance parameters (g factors and hyperfine structure constants) and local structures are theoretically investigated for Cu2+ in alkali lead tetraborate 90R2B4O7·9PbO·CuO (R = Li, Na and K) glasses based on the high-order perturbation calculations for a tetragonally elongated octahedral 3d9 complex. The [CuO6]10? complexes are found to experience the relative tetragonal elongation ratios 18%, 23% and 30% for R = Li, Na and K, respectively, due to the Jahn–Teller effect, much larger than those for similar ARbB4O7 (A = Li, Na and K) glasses. This point is attributed to the lattice expansion (longer A–O bond lengths) with doped PbO, yielding lower force constants and more intense Jahn–Teller elongations in the 90R2B4O7·9PbO·CuO glasses. The increasing tendency (Li > Na > K) of the relative elongation ratio λ, covalency and the ratio Δg///Δg⊥ for g-shifts are systematically analysed in a uniform way. 相似文献
993.
994.
Ni nanoparticles (Ni(1) and Ni(2)) and Ni loaded SiMCM‐41 (15Ni/SiMCM‐41) were prepared and characterized with XRD, TEM, N2 adsorption, CO chemisorption, and H2‐TPR. The Ni specific surface area followed the order of 15Ni/SiMCM‐41 > Ni(1) >> Ni(2), whereas the Ni particle size exhibited the opposite trend. These catalysts were utilized for vapour phase hydrogenation of cinnamaldehyde at 1 atm and 200 °C in a fixed‐bed, down flow reactor. The main products include hydrocinnamaldehyde, styrene, ethylbenzene, and 2‐phenyl‐1‐propanol. The catalytic activity decreased in the same order as that of Ni specific surface areas. The SiMCM‐41 support possessed very large surface area, leading to enhanced dispersion and specific surface area of Ni nanoparticles. As a result, the 15Ni/SiMCM‐41 catalyst exhibited the highest activity. Based on the investigation of reaction pathways, it is important to emphasize that both hydrogenation and hydroelimination of formaldehyde (hydrodeformylation) occur in the vapour phase reaction. 相似文献
995.
996.
One-pot simultaneous debrominative decarboxylation and sulfamation of anti-2,3-dibromo-3-(4-chlorosulfonylphenyl)propanoic acid in DMF (for alkyl amines) or DMF-pyridine (for aryl amines) using a diverse range of alkyl and aryl amines under microwave irradiation condition stereoselectively afforded (Z)-4-(2-bromovinyl)benzenesulfonamides in good yields. 相似文献
997.
998.
本文提出了一种计算多电荷离子与原子碰撞中K壳层电子俘获截面的新方法,称为模型势Oppenheimer-Brinkman-Krammer近似(MPOBK)。在该方法中我们用模型势来描述K电子所处的有效场,同时在波函数中考虑屏蔽效应。我们得到的K壳层总俘获截面是一个表解析达式。对H~ 、He~(2 )-Ne,H~ 、He~(2 )-C及O~(5 ,6 )-Ar体系的计算表明本文结果较好地与实验数据一致。 相似文献
999.
Wyttenbach T Paizs B Barran P Breci L Liu D Suhai S Wysocki VH Bowers MT 《Journal of the American Chemical Society》2003,125(45):13768-13775
1000.