Similarity Measures of Satellite Images Using an Adaptive Feature Contrast Model

Similarity measurement is one of key operations to retrieve “desired” images from an image database. As a famous psychological similarity measure approach, the Feature Contrast (FC) model is defined as a linear combination of both common and distinct features. In this paper, an adaptive feature contrast (AdaFC) model is proposed to measure similarity between satellite images for image retrieval. In the AdaFC, an adaptive function is used to model a variable role of distinct features in the similarity measurement. Specifically, given some distinct features in a satellite image, e.g., a COAST image, they might play a significant role when the image is compared with an image including different semantics, e.g., a SEA image, and might be trivial when it is compared with a third image including same semantics, e.g., another COAST image. Experimental results on satellite images show that the proposed model can consistently improve similarity retrieval effectiveness of satellite images including multiple geo-objects, for example COAST images.

Photocatalyzed ditrifluoromethylthiolation of alkenes with CF_(3)SO_(2)Na

Since the first report of sodium trifluoromethanesulfinate(CF_(3)SO_(2)Na) as an electrophilic trifluoromethylthiolation reagent in 2015,there has been no breakthrough in research in this field.Herein,we disclose an unprecedented usage of CF_(3)SO_(2)Na as a radical trifluoromethylthiolation reagent.A photocatalyzed ditrifluoromethylthiolation of alkenes with CF_(3)SO_(2)Na in the presence of PPh_(3) and catalytic copper has been developed.Interestingly,either Ir[(p-Fppy)_(2)(bpy)]PF_6 or Ir(ppy)_(3) could facilitate this transformation.Mechanistic studies indicate that initiation of the radical chain proceeded via two different photocatalytic quenching mechanisms.This protocol provides a practical method for the construction of diverse vicinal ditrifluoromethylthiolated compounds.

Lignin-derived Zn single atom/N-codoped porous carbon forα-alkylation of aromatic ketones with alcohols via borrowing hydrogen strategy

A green and scalable strategy has been developed for the synthesis of lignin-derived Zn single atom/N-codoped porous carbon(LCN@Zn-SAC)containing similar ZnNx sites with carbonic anhydrases.This catalyst exhibits superior activity on theα-alkylation of ketones with alcohols via borrowing hydrogen strategy(TON up to 15 h^(−1))than most of previously reported works.The dehydrogenation of benzyl alcohol is the rate-determining step based on kinetic experiment results.According to experimental and theoretical calculation results,Zn electron density is inversely proportional to reaction energy barriers,because Zn sites with less positive charge(ZnN_(4) and ZnN_(3)C)in Zn-SACs display better borrowing hydrogen ability than other Zn sites.Furthermore,this catalyst can be recycled by simple centrifugation,which can be reused at least 8 runs with no obvious lose in activity.To the best of our knowledge,this is the first example of non-noble metal-SAC-catalyzedα-alkylation via borrowing hydrogen strategy.

Chemoselective desulfurization-fluorination/bromination of carbonofluoridothioates for the O-trifluoromethylation and O-bromodifluoromethylation of alcohols

Herein,a method for synthesizing various alkyl trifluoromethyl and alkyl bromodifluoromethyl ethers using carbonofluoridothioates(R-OC(=S)F)as precursors has been described.Carbonofluoridothioates were obtained upon the reaction of an alcohol and S=CF_(2) generated via the decomposition of an SCF_(3) anion,and then selectively transformed into their corresponding trifluoromethyl and bromodifluoromethyl ethers upon changing the reaction conditions.This transformation has also been extended to the one-pot,two-step conversion of alcohols into alkyl trifluoromethyl ethers.A series of alkyl bromodifluoromethyl ethers has also been synthesized.These compounds open up a new avenue for the synthesis of a wide range of useful fluorinated products.In addition,this method is suitable for the late-stage introduction of trifluoromethyl ethers in complex small molecules.

Photocatalyzed Dual-Oxidative Trifluoromethylthio-Trifluoromethylation of Alkenes with CF3SO2Na

A novel photocatalyzed trifluoromethylthio-trifluoromethylation of alkenes has been developed,using CF_(3)SO_(2)Na as both CF_(3) and SCF_(3) source.This photocatalyzed dual-oxidative strategy,which combines two parallel oxidative events,provides a facile method to synthesize a series of vicinal trifluoromethylthio-trifluoromethylated compounds.This reaction is operationally simple,proceeds under mild conditions and exhibits exceptional substrate generality and functional group compatibility.