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Daniel T. Valentine 《国际流体数值方法杂志》1995,21(2):155-180
The disarrangement of a perturbed lattice of vortices was studied numerically. The basic state is an exponentially decaying, exact solution of the Navier-Stokes equations. Square arrays of vortices with even numbers of vortex cells along each side were perturbed and their evolution was investigated. Whether the energy in the perturbation grows somewhat before it decays or decays monotonically depends on the initial strength of the vortices of the basic state, the extent of lateral confinement and the structure of the perturbation. The critical condition for temporally local instability, i.e. the critical amplitude of the basic state that must be exceeded to allow energy transfer from the basic state to the perturbation, is discussed. In the strongly confined case of a square lattice of four vortices the appearance of enchancement of global rotation is the result of energy transfer from the basic state to a temporally local unstable mode. Energy is transferred from the basic state to larger-scaled structures (inverse cascade) only if the scales of the larger structures are inherently contained in the initial structure of the perturbation. The initial structure of the double array of vortices is not maintained except for a very special form of perturbation. The facts that large scales decay more slowly than small scales and that, when non-linearities are sufficiently strong, energy is transferred from one scale to another explain the differences in the disarrangement process for different initial strengths of the vortices of the basic state. The stronger vortices, i.e. the vortices perturbed in a manner that increases their strength, tend to dominate the weaker vortices. The pairing and subsequent merging (or capture) of vortices of like sense into larger-scale vortices are described in terms of peaks in the evolution of the square root of the palinstrophy divided by the enstrophy. 相似文献
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Daniil A. Boiko Evgeniy O. Pentsak Vera A. Cherepanova Evgeniy G. Gordeev Valentine P. Ananikov 《Chemical science》2021,12(21):7428
Smoothness/defectiveness of the carbon material surface is a key issue for many applications, spanning from electronics to reinforced materials, adsorbents and catalysis. Several surface defects cannot be observed with conventional analytic techniques, thus requiring the development of a new imaging approach. Here, we evaluate a convenient method for mapping such “hidden” defects on the surface of carbon materials using 1–5 nm metal nanoparticles as markers. A direct relationship between the presence of defects and the ordering of nanoparticles was studied experimentally and modeled using quantum chemistry calculations and Monte Carlo simulations. An automated pipeline for analyzing microscopic images is described: the degree of smoothness of experimental images was determined by a classification neural network, and then the images were searched for specific types of defects using a segmentation neural network. An informative set of features was generated from both networks: high-dimensional embeddings of image patches and statics of defect distribution.Defectiveness of carbon material surface is a key issue for many applications. Pd-nanoparticle SEM imaging was used to highlight “hidden” defects and analyzed by neural networks to solve order/disorder classification and defect segmentation tasks. 相似文献
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Valentine G Nenajdenko Georgy N Varseev Alexey V Shastin 《Journal of fluorine chemistry》2003,124(1):115-118
A novel catalytic approach to (2,2-difluorovinyl)benzenes has been developed. It was found that hydrazones of aromatic aldehydes generated in situ could be converted to the corresponding (2,2-difluorovinyl)benzenes by catalytic olefination reaction (COR) with dibromodifluoromethane in the presence of CuCl. 相似文献
6.
Valentine G. Nenajdenko Sergey V. Druzhinin Elizabeth S. Balenkova 《Tetrahedron letters》2005,46(51):8853-8855
Reactions of α,β-unsaturated CF3-ketones with nitromethane and ethyl nitroacetate have been investigated. We found that α,β-unsaturated trifluoromethylketones react with ethyl nitroacetate in the presence of calcinated potassium fluoride to form two classes of 1,4-conjugated addition products: CF3-γ-nitroketones and 6,6,6-trifluoro-2-nitro-5-oxohexanoates in nearly quantitative yields. The products obtained are precursors for CF3-pyrrolidine synthesis. 相似文献
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Reaction of the amines (CF3)2NX (X=Cl,Br) with norbornadiene either in solvent (CH2Cl2) at ?78 °C in the dark or in the vapour phase at 20 °C in daylight gives a mixture of 3-halogeno-5-(-bistrifluoromethylamino)nortricyclene (, -and , -isomers) and -5-(-bistrifluoromethylamino)- -7-halogenonorbornene in quantitative yield formed halonium ion addition to the diene. The reaction of the amine (CF3)2NBr in solvent Me2O or Et2O at ?78 °C in the dark gives the same products in low yield, together with 3-bromo-5-alkoxynortricyclene (, - and , -isomers) and the amine (CF3)2NR (R=Me, Et) in high yield. 相似文献
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Srigokul Upadhyayula Vicente Nu?ez Eli M. Espinoza Jillian M. Larsen Duoduo Bao Dewen Shi Jenny T. Mac Bahman Anvari Valentine I. Vullev 《Chemical science》2015,6(4):2237-2251
Cyanine dyes are broadly used for fluorescence imaging and other photonic applications. 3,3′-Diethylthiacyanine (THIA) is a cyanine dye composed of two identical aromatic heterocyclic moieties linked with a single methine, –CH. The torsional degrees of freedom around the methine bonds provide routes for non-radiative decay, responsible for the inherently low fluorescence quantum yields. Using transient absorption spectroscopy, we determined that upon photoexcitation, the excited state relaxes along two parallel pathways producing three excited-state transients that undergo internal conversion to the ground state. The media viscosity impedes the molecular modes of ring rotation and preferentially affects one of the pathways of non-radiative decay, exerting a dominant effect on the emission properties of THIA. Concurrently, the polarity affects the energy of the transients involved in the decay pathways and further modulates the kinetics of non-radiative deactivation. 相似文献
10.
Atom-economic Approach to the Synthesis of α-(Hetero)aryl-substituted Furan Derivatives from Biomass
Leonid V. Romashov Kirill S. Kozlov Matvey K. Skorobogatko Alexander Y. Kostyukovich Valentine P. Ananikov 《化学:亚洲杂志》2022,17(1):e202101227
An atom-economic ring construction approach to the synthesis of α-(hetero)arylfurans based on renewable furanic platform chemicals has been developed. Corresponding compounds have been prepared in good to excellent yields via [2+2+2] and [4+2] cycloaddition reactions using metal-catalyzed or photoredox protocols. Easily available HMF-based 2-hydroxymethyl-5-ethynylfuran and 2-hydroxymethyl-5-cyanofuran were used as starting materials. A synthetic route with an improved carbon economy factor has been implemented to achieve sustainability aim. The possible application of arylfurans as molecular conductors has been investigated by DFT calculations, which revealed excellent charge transfer properties. As a future perspective, integration of biomass processing strategy into manufacturing of molecular electronics was pointed out to achieve the aim of sustainability. 相似文献