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thermodynamic effects on Particle Movement:Wind Tunnel Simulation Results

Chinese Geographical Science 2012年第2期22卷 178-187页

作者： NIU Qinghe QU Jianjun ZHANG Kecun LIU Xianwan Key Laboratory of Desert and Desertification Cold and Arid Regions Environmental and Engineering Research Institute Chinese Academy of Sciences Lanzhou 730000 China Dunhuang Gobi and Desert Research Station Cold and Arid Regions Environmental and Engineering Research Institute Chinese Academy of Sciences Dunhuang 736200 China Gansu Center for Sand Hazard Reduction Engineering and Technology Lanzhou 730000 China

Sand/dust storms are some of the main hazards in arid and semi-arid zones. These storms also influence global environmental changes. By field observations, empirical statistics, and numerical simulations, pioneer researchers on these natural events have concluded the existence of a positive relationship between thermodynamic effects and sand/dust storms. thermodynamic effects induce an unsteady stratified atmosphere to influence the process of these storms. However, studies on the relationship of thermodynamic effects with particles (i.e., sand and dust) are limited. In this article, wind tunnel with heating was used to simulate the quantitative relationship between thermodynamic effects and particle movement on different surfaces. Compared with the cold state, the threshold wind velocity of particles is found to be significantly decrease under the hot state. The largest decrease percentage exceedes 9% on fine and coarse sand surfaces. The wind velocity also has a three-power function in the sand transport rate under the hot state with increased sand transport. thermodynamic effects are stronger on loose surfaces and fine particles, but weaker on compacted surfaces and coarse particles.

关键词： thermodynamic effect threshold wind velocity nel simulation drifting sand flux structure sand transport rate wind tunnel simulation

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NUMERICAL STUDY ON THE DYNAMIC AND thermodynamic effectS OF THE QINGHAI-XIZANG PLATEAU ON THE SEASONAL TRANSITION IN THE EARLY SUMMER IN EAST ASIA

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Acta meteorologica Sinica 1995年第1期9卷 35-47页

作者：郑庆林吴军 Chinese Academy of Meteorological Sciences Beijing 100081

By employing a five-layer seasonal numerical weather prediction model and utilizing the National Meteorological Center (NMC) objective analysis data on May 10,1991 as the initial field,three numerical experiments——diabatic with orography,adiabatic with orography and adiabatic without orography——have been carried out to investigate the dy- namic and thermodynamic effects of the Qinghai-Xizang Plateau (hereafter the Plateau) on the seasonal transition in the early summer in East *** results show that the typical seasonal transition features such as the northward shift of the subtropical westerly jet stream,the adjustment of the long-wave in middle and high latitudes and the changes of the circulation in the lower troposphere can be well simulated,if the dynamic and thermodynamic effects of the Plateau are both considered in the model as in the experiment adiabatic with *** other two experiments,it is failed to simulate out the seasonal transition features. The results also show that the thermodynamic effect of the Plateau acts on the atmosphere as a gradually enhanced heating source in the early summer,which makes the air temperature in 500 hPa over the Plateau increase by nearly 10℃ in a month and accelerates the northward shift of the subtropical westerly jet stream about seven latitudes more north- ward in twenty days and helps the shifted jet maintain at the northern periphery of the *** is also helpful to the formation and maintenance of the Lake Balchas trough and the northward and westward extension of the Pacific subtropical *** the other hand,the dynamic effect of the Plateau weakens the northward shift of the subtropical westerly jet stream and barricades the westward extension of the Pacific subtropical *** only the dynamic effect of the Plateau is considered in the model without consideration of the thermodynamic effect of the Plateau,not only the shifted jet withdraws southward but also the simulated Lake Balchas trough is 10

关键词： seasonal transition Qinghai-Xizang Plateau dynamic effect thermodynamic effect

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Computational insights into the effects of reagent structure and bases on nucleophilic monofluoromethylation of aldehydes

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Chinese Chemical Letters 2022年第5期33卷 2387-2390页

作者： Meng-Meng Zheng Hao-Dong Tan Yueqian Sang Xiao-Song Xue Jin-Pei Cheng State Key Laboratory of Elemento-Organic Chemistry College of ChemistryNankai UniversityTianjin 300071China Key Laboratory of Organofluorine Chemistry Shanghai Institute of Organic ChemistryUniversity of Chinese Academy of SciencesChinese Academy of SciencesShanghai 200032China Center of Basic Molecular Science Department of ChemistryTsinghua UniversityBeijing 100084China

Although fluorobis(phenylsulfonyl)methane(FBSM)and its cyclic analog 2-fluoro-1,3-benzodithiole-1,1,3,3-tetraoxide(FBDT)possess similar physicochemical properties,Shibata et *** that FBSM failed to undergo nucleophilic monofluoromethylation of aldehydes regardless of the reaction conditions at-tempted(using various organic and inorganic bases).However,it was later discovered by Hu et *** the nucleophilic monofluoromethylation could be accomplished by employing lithium hexamethyldisi-lazide(LiHMDS)as a ***,we present an in-depth computational investigation into the intrigu-ing effects of reagent structure and bases on the nucleophilic monofluoromethylation of *** computations reveal the 1,4-diazabicyclo[2.2.2]octane(DABCO)catalyzed nucleophilic monofluoromethy-lation of benzaldehyde with acyclic FBSM is a thermodynamically unfavorable process mainly due to the destabilizing O···O lone pair repulsions in FBSM product,whereas such repulsion could be largely avoided in FBDT product because of its constrained five-membered ring *** LiHMDS as a base can not only facilitate the nucleophilic monofluoromethylation via Li–O interactions but also render the monofluoromethylation of benzaldehyde with FBSM thermodynamically favored.

关键词： Nucleophilic monofluoromethylation Fluoroalkylation reagent DFT calculations thermodynamic effect Lone pair repulsion

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