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21.
Streaks play a major role in the process of turbulent generation. Numerous studies have been performed to characterize them,
most of which used only single point measurements and only a few characteristics were studied. To investigate the streaks
in more detail, a stereoscopic particle image velocimetry (SPIV) experiment was conducted to record 2D3C velocity fields in
ten planes parallel to the wall from y
+ = 14.5 to y
+ = 48 at Reynolds number Re
θ = 7,800 in a fully developed turbulent boundary layer along a flat plate. This study develops a method based on pattern recognition
to detect streaks from velocity fields obtained by SPIV and characteristizes them in depth. The results are in good agreement
with the previous studies and expand significantly the information about the characteristics of the streaks. 相似文献
22.
Ren Milcent Jean-Claude Malanda Go Barbier Jacqueline Vaissermann 《Journal of heterocyclic chemistry》1997,34(1):329-336
Reactions of ethyl 3-aryl-2-benzoylpropenoates 1 with guanidine and N-alkyl(or benzyl)guanidines have been investigated. Ethyl 2-aminodihydro-5-pyrimidinecarboxylate derivatives 3, 4 or 5, and 3,7-diethoxy-carbonyl-4,6-dihydro-2,4,6,8-tetraaryl-1H-pyrimido[1,2-a]pyrimidines 6 have been synthesized. 相似文献
23.
This review provides an overview of the various synthetic pathways of the N-CF3 group. This pattern can be generated either from fluoride ions or from electrophilic, nucleophilic, or radical trifluoromethylation. This article mainly focuses on the most recent and prominent studies. 相似文献
24.
Félicité?Pacifique?Mutuyimana Juanjuan?Liu Min?Na Stanislas?Nsanzamahoro Zhi?Rao Hongli?Chen Xingguo?ChenEmail author 《Mikrochimica acta》2018,185(11):518
The authors describe a method for the preparation of orange-red emissive carbon dots (CDs) with excitation/emission peaks at 520/582 nm. The CDs were hydrothermally prepared by a one-pot strategy from trimesic acid and 4-aminoacetanilide. The fluorescence of the CDs is strongly quenched by hydrogen peroxide. The oxidation of glucose by glucose oxidase (GOx) produces H2O2 that quenches the fluorescence via static quenching. Based on this phenomenon, a fluorometric method was established for the determination of glucose. Under the optimum conditions, response is linear in the 0.5 to 100 μM glucose concentration range, with a 0.33 μM limit of detection. The method is selective for glucose over its analogues and was successfully applied to the determination of glucose in diluted human serum and in urine from diabetics and healthy individuals. Recoveries from spiked samples range from 98.7 to 102.5%. 相似文献
25.
Rauter AP Fernandes AC Czernecki S Valery JM 《The Journal of organic chemistry》1996,61(11):3594-3598
A five-step synthesis from 3 leading to a partially protected amipurimycin sugar moiety 14 in an overall yield of 47% is described and includes deoxygenation at C-4 and regio- and stereoselective construction of the branched chain. Deoxygenation at C-4 of 3 was possible by three different methods. Radical reduction with tri-n-butyltin hydride of the appropriate phenoxythiocarbonyl derivative afforded the desired deoxysugar 5 in 47% overall yield together with the secondary products 6 and 7 due to depivaloylation at C-2 and elimination of methanol. The most adequate deoxygenation procedure used the system Ph(3)P/I(2)/imidazole which led to the preparation of 5 in one step in 61% yield. When the system Ph(3)PBr(2)/Ph(3)P was tried, only 8 was formed due to elimination of methanol. The synthesis of 5 was then accomplished by reaction of 8 with methanol in the presence of triphenylphosphine hydrobromide in 37% overall yield. Branched-chain construction was accomplished by Wittig reaction of 5 with [(ethoxycarbonyl)methylene]triphenylphosphorane, followed by osmilation and reduction with lithium aluminum hydride. Isopropylidenation of 14 afforded 16 with a free hydroxy group at C-6 for chain elongation and further synthesis of amipurimycin. 相似文献
26.
The oxidation of aldehyde semicarbazones with lead dioxide in acid media was effected. The 4,4-disubstituted semicarbazones of aromatic aldehydes afford 2-amino-1,3,4-oxadiazole derivatives. The 2,4-disubstituted semicarbazones give 2,4-dihydro-1,2,4-triazol-3-ones, often in higher yields than the known methods. The mechanisms for the formation of these compounds are proposed. 相似文献
27.
G. Süss-Fink Hong Yan G. V. Nizova S. Stanislas G. B. Shul'pin 《Russian Chemical Bulletin》1997,46(10):1801-1803
Methane is oxidized in aqueous solution with atmospheric oxygen and hydrogen peroxide in a reaction catalyzed by a NaVO3-pyrazine-2-carboxylic acid system. Methyl hydroperoxide is selectively formed at 50°C. The turnover number of the catalyst
after 24 h amounts to 480, and the yield of methyl hydroperoxide is 24% with respect to H2O2. Formaldehyde and formic acid are mainly formed at 120°C.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1897–1899, October, 1997. 相似文献
28.
Abdeltif Bourhim Stanislas Czernecki Pierre Krausz Alain Viari Paul Vigny 《Journal of carbohydrate chemistry》2013,32(5):761-765
ABSTRACT Although the phenomenon is not fully understood, it is now well established that some porphyrins have a natural tendency to concentrate more in malignant tumors than in normal tissue. This property has found an application in photodynamic therapy of cancers in which a tumor, with an enriched concentration of porphyrin, can be selectively destroyed by applying light, without damage to surrounding cells.1 相似文献
29.
ABSTRACT The Witting reaction of (carbethoxymethylene)triphenylphosphorane with perbenzylated sugar δ-lactones and their 2-acetamido-2-deoxy derivatives is described. It is shown that this olefination occurred readily with the galacto and gluco derivatives, leading stereoselectively to Z-C-glycosylidenes in good yields. However, the same reaction with the perbenzylated 2-deoxy-D-arabino-hexono-1,5-lactone and the mannonolactones worked poorly. Reduction over Pd/C followed by acetylation of the obtained C-glycosylidenes led stereoselectively to peracetylated β-C-glycosides and amino β-C-glycosides. The olefin function could also be reduced selectively by Raney nickel or NiCl2/NaBH4, affording the perbenzylated C-glycosides and amino β-C-glycosides. Other transformation of the enol ether function is also reported. 相似文献
30.
Entropy solutions for nonlinear nonhomogeneous Neumann problems involving the generalized p(x)-Laplace operator 下载免费PDF全文
Elhoussine Azroul Mohamed Badr Benboubker Stanislas Ouaro 《Journal of Applied Analysis & Computation》2013,3(2):105-121
In this work we investigate a class ofnonlinear p(x) Laplace problems with Neumann nonhomoge-neous boundary conditions and L1 data. The techniques of entropy solutions for elliptic equationsare used to prove the existence of a solution. 相似文献