Asymmetric Michael Addition of Aldimino Esters with Chalcones Catalyzed by Silver/Xing‐Phos: Mechanism‐Oriented Divergent Synthesis of Chiral Pyrrolines

The mechanism‐oriented reaction design for the divergent synthesis of chiral molecules from simple starting materials is highly desirable. In this work, aromatic amide‐derived nonbiarylatropisomer/silver (silver/Xing‐Phos) complex was used to catalyze the Michael addition of glycine aldimino esters to chalcones and successfully applied to the subsequent cyclocondensation to afford substituted cis‐Δ(1)‐pyrroline derivatives with up to 98 % ee. Besides the inherent performance of the chiral Ag/Xing‐Phos catalyst system, it was found that the workup of such reactions played an important role for the stereoselective construction of stereodivergent Δ(1)‐pyrrolines, in which an epimerization of the cis‐Δ(1)‐pyrrolines to the trans‐isomers during was revealed.     

Comparison of performance between rescaled range analysis and rescaled variance analysis in detecting abrupt dynamic change

In the present paper, a comparison of the performance between moving cutting data-rescaled range analysis(MCR/S) and moving cutting data-rescaled variance analysis(MC-V/S) is made. The results clearly indicate that the operating efficiency of the MC-R/S algorithm is higher than that of the MC-V/S algorithm. In our numerical test, the computer time consumed by MC-V/S is approximately 25 times that by MC-R/S for an identical window size in artificial data. Except for the difference in operating efficiency, there are no significant differences in performance between MC-R/S and MC-V/S for the abrupt dynamic change detection. MC-R/S and MC-V/S both display some degree of anti-noise ability. However, it is important to consider the influences of strong noise on the detection results of MC-R/S and MC-V/S in practical application processes.     

The spatial-temporal evolution of coherent structures in log law region of turbulent boundary layer

The spatial-temporal evolution of coherent structures(CS) is significant for turbulence control and drag reduction. Among the CS, low and high speed streak structures show typical burst phenomena. The analysis was based on a time series of three-dimensional and three-component(3D-3C) velocity fields of the flat plate turbulent boundary layer(TBL) measured by a Tomographic and Time-resolved PIV(Tomo TRPIV) system. Using multi-resolution wavelet transform and conditional sampling method, we extracted the intrinsic topologies and found that the streak structures appear in bar-like patterns. Furthermore, we seized locations and velocity information of transient CS, and then calculated the propagation velocity of CS based on spatial-temporal cross-correlation scanning. This laid a foundation for further studies on relevant dynamics properties.