飞机着陆下沉速度最大值的确定方法

飞机着陆下沉速度是起落架设计和飞机设计定型试飞的起落架强度检查中的最主要的参数之一.本文按军用飞机强度和刚度规范中规定的要求,通过对皮尔逊Ⅲ型概率密度分布函数的推导,完成了在不同偏态系数Cs下的离均系数Φp和超越概率P的对应数值编程计算,并得到了相应的计算结果.据此可以确定各类飞机在各种着陆类型下的着陆下沉速度的最大值.这对飞机的设计研究提供指导.     

A Sensitive “Optical Nose” for Detection of Volatile Organic Molecules Based on Au@MOFs Nanoparticle Arrays through Surface-Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) is an effective technique for detecting toxic gas and volatile organic molecules (VOMs); however, recent SERS-based gas sensors have disadvantages and lack an effective approach to capture toxic gas and insufficient reproducibility of SERS substrates. Herein, a facile strategy is developed to integrate metal-organic frameworks with Au nanoparticle (NP) arrays to form Au@ZIF-8 NP arrays, which can be used as an “optical nose” based on SERS to detect toxic VOMs with good reproducibility and sensitivity. Toluene as a target molecule is recognized at ppm levels by the Au@ZIF-8 NP arrays in situ. And the analytical enhancement factor of Au@ZIF-8 NP arrays for toluene is about 1.2 × 10⁵. Importantly, this SERS substrate can also detect the 1-butanol molecule, which provides an idea for designing a universal VOM sensor. In addition, the coating method of the ZIF-8 shell can be extended to synthetize various NPs@ZIF-8 core–shell composites, such as Au nanospheres@ZIF-8, Au@Ag nanorods@ZIF-8, PS microspheres@ZIF-8, and Fe₂O₃ microellipsoids@ZIF-8 composites.     

Unraveling the Mechanism of the IrIII-Catalyzed Regiospecific Synthesis of α-Chlorocarbonyl Compounds from Allylic Alcohols

We have used experimental studies and DFT calculations to investigate the Ir^III-catalyzed isomerization of allylic alcohols into carbonyl compounds, and the regiospecific isomerization–chlorination of allylic alcohols into α-chlorinated carbonyl compounds. The mechanism involves a hydride elimination followed by a migratory insertion step that may take place at Cβ but also at Cα with a small energy-barrier difference of 1.8 kcal mol⁻¹. After a protonation step, calculations show that the final tautomerization can take place both at the Ir center and outside the catalytic cycle. For the isomerization–chlorination reaction, calculations show that the chlorination step takes place outside the cycle with an energy barrier much lower than that for the tautomerization to yield the saturated ketone. All the energies in the proposed mechanism are plausible, and the cycle accounts for the experimental observations.