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The SiC single-crystal substrate with ultrasmooth and damage-free properties has potential applications in the field of optoelectronics and microelectronics. Lapping is one of the important processes for ultraprecision machining of the SiC single-crystal substrate. The lapping quality has an important impact on the surface quality, processing time, processing cost and processing efficiency of the subsequent chemical mechanical polishing (CMP) of the SiC single-crystal substrate. In this paper, four kinds of lapping pastes with different ingredients were prepared. The tribochemical action and mechanism of the oxidant in the lapping paste were studied. The results show that NaOH can be used as an oxidant for the tribochemical mechanical lapping of the SiC single crystal. Under the catalysis of iron oxide and frictional force, the tribochemical reaction between the SiC single-crystal substrate and the oxidant NaOH occurred and the silicon oxides (such as SiO[Formula: see text], gaseous carbon oxides and other reactants were produced. The surface energy of the SiC substrate was reduced and the material removal rate was improved effectively. These results can provide a reference for further research on the mechanism of tribochemical mechanical lapping.

To improve the efficiency and surface quality in tribochemical mechanical lapping of 6H–SiC single-crystal substrate, the effects of oxidant type, content and abrasive size on the material removal rate (MRR) and surface roughness were studied in this paper. The results show that different oxidants have their maximum of material removal rate at their respective optimum content, namely 1768 nm/min for 10% wt sodium hydroxide, 1382 nm/min for 5% wt potassium permanganate and 1271 nm/min for 5% wt dichromium trioxide, respectively. However, the types and contents of oxidants have little effect on the surface roughness of SiC after lapping. Therefore, 10% wt NaOH was chosen as the oxidant of tribochemical mechanical lapping paste for lapping 6H–SiC single-crystal substrate. The abrasive size had a great influence on the material removal rate in lapping 6H–SiC single-crystal substrate. When the abrasive size is 28 µm in diameter, the material removal rate reaches the maximum value, but the surface roughness also is the maximum value after lapping. Then, the composition of optimized lapping paste was obtained. Research results show that the larger the abrasive using in lapping paste is, the larger the MRR and surface roughness are in certain range. The tribochemical reactions on the surface of SiC will occur and oxides of SiO2 or Si(OH)4 or Na2SiO3 or the compound of SiO2, Na2SiO3 and Si(OH)4 produced on the surface of SiC will be removed by the abrasives.

During vertebrate embryogenesis, the cranial neural crest (CNC) forms at the neural plate border and subsequently migrates and differentiates into many types of cells. The transcription factor Snail2, which is induced by canonical Wnt signaling to be expressed in the early CNC, is pivotal for CNC induction and migration in Xenopus. However, snail2 expression is silenced during CNC migration, and its roles at later developmental stages remain unclear. We generated a transgenic X. tropicalis line that expresses enhanced green fluorescent protein (eGFP) driven by the snail2 promoter/enhancer, and observed eGFP expression not only in the pre-migratory and migrating CNC, but also the differentiating CNC. This transgenic line can be used directly to detect deficiencies in CNC development at various stages, including subtle perturbation of CNC differentiation. In situ hybridization and immunohistochemistry confirm that Snail2 is re-expressed in the differentiating CNC. Using a separate transgenic Wnt reporter line, we show that canonical Wnt signaling is also active in the differentiating CNC. Blocking Wnt signaling shortly after CNC migration causes reduced snail2 expression and impaired differentiation of CNC-derived head cartilage structures. These results suggest that Wnt signaling drives the re-expression of snail2 in the post-migratory CNC and regulates CNC differentiation.

For the part of collection and transmission field data of the agriculture expert system, this paper mainly design a kind of bluetooth module. It based on the technology of the data collection and transmission of the Bluetooth chip. So we can realize the wireless transferring between 10m and 100m, and then achieve the goal of deal with the Real-time monitoring of field data using mobile phones.