Controlling positional selectivity
represents one of the most important
aspects in transition-metal-catalyzed C–H bond functionalization.
However, the conventional directing template strategies via a covalent
binding to the substrates are always hindered by prior stoichiometric
installation and removal of the directing groups. Herein, we report
a palladium-catalyzed meta-selective C–H olefination
of aromatic carbonyl compounds by noncovalent hydrogen-bonding interaction.
N,N′-Substituted ureas were engineered to serve as a H-bonding
donor for binding to the substrates and, meanwhile, achieve site-selective
control by the integrated directing group.
Mountains and highlands serve as "water towers" as they provide downstream alluvial plains and lowlands with freshwater (Viviroli & Weingartner, 2008). The Himalayas are the source of water for all of the major rivers in southeast Asia and play a significant role in supplying freshwater for the vast lowland areas of China, India, Bhutan, Nepal and Pakistan (Bookhagen, 2012;Fan et al., 2019). These Himalayan "water towers" are closely related to human welfare and ecosystem health because of their role in generating runoff, groundwater recharge, providing flow to the lowlands through river networks and aquifers, transporting nutrients from porous media to the rivers which affects the biological cycle (Connolly et al., 2020), and sustaining both natural terrestrial and aquatic habitats (i.e., forests and lakes) and artificial infrastructure
Schlieren and shadowgraph photography has been widely used to offer insight into the flow field in aerospace engineering due to their ease of application. The high-speed schlieren and shadowgraph techniques are typically applied to investigation of unsteady shock wave structure including shock reflection patterns and shock wave/boundary layer interactions, etc. Generally, qualitative analysis is performed based on the schlieren and shadowgraph image sequences. To process and analyze the large data set of the high-speed schlieren and shadowgraph images quantitatively, especially for the shock wave detection and tracking, a software was developed based on MATLAB GUI and its image processing toolbox. In this study, the image processing techniques exploited in the software, such as background subtraction, filter, threshold, edge detection, and shock tracking are presented. A case study on the phenomena of shock wave reflection from a solid surface was conducted. The results show that the proper filter method and the background image subtraction can effectively eliminate the image noises in frequency domain, which makes it easier to analyze the flow structure. Moreover, the instantaneous locations of shock waves are detected accurately, and the shock wave propagation speed calculated using the developed software are consistent with those of previous studies.
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