Hydrodynamic lubrication of rectangular micro-textures on sliding contact surfaces is investigated using numerical calculation methods. The theoretical models for the slider surface are developed and the film pressure is used to evaluate the hydrodynamic lubrication based on the Reynolds equation. Meanwhile, the geometry and distribution of the rectangular dimples are optimized for maximizing the average film pressure. Results show that the film pressure is dependent on the geometry and distribution of the rectangular micro-dimples. The optimal geometry of the single rectangular dimple is obtained, and the spacing has an important influence on the film pressure. The distribution types of rectangular dimples affect the hydrodynamic lubrication significantly and the interlaced array of the rectangular micro-dimples is beneficial to enhancing the hydrodynamic lubrication. Meanwhile, the rectangular dimples with 72° interlaced angle exhibits the best effectivity.
Nature has always been recognized as a rich source for the identification of new drug candidates. Heliannuols have drawn wide attention because of their interesting structural scaffolds and biological potential. Biological evaluation has shown that heliannuols have the allelopathic activity and may be used as lead compounds in herbicides. The synthesis of this family of molecules has always been challenging because of their unique scaffold and multiple chiral centers. Up to now, there have been 32 synthetic routes toward these kinds of natural compounds and a mini-review; however, the synthesis of heliannuols F, I, and J have not been reported yet. Many different strategies such Julia coupling, Dickman condensation, ring-closing metasis, ring contraction or expansion, rearrangement, and intramolecular epoxide opening have been employed in these syntheses. More efficient and highly enantiocontrolled and ecofriendly strategies should be developed for sustainable chemistry. 相似文献