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121.
In self-preserving turbulent wall flows, both measurements and direct numerical simulations indicate that the mean square vorticity in the outer region does not depend only on and U
. It also depends on the Reynolds number.RAA is grateful to St. Francis Xavier University (Antigonish) for their support while on study leave there. The support of ARC is gratefully appreciated. 相似文献
122.
Synthesis and electrochemical and photophysical studies of tetrathiafulvalene-annulated phthalocyanines 总被引:1,自引:0,他引:1
Loosli C Jia C Liu SX Haas M Dias M Levillain E Neels A Labat G Hauser A Decurtins S 《The Journal of organic chemistry》2005,70(13):4988-4992
The synthesis of tetrakis(tetrathiafulvalene)-annulated metal-free and metallophthalocyanines 5-8 via the tetramerization of the phthalonitrile derivative 4 is reported. All of them have been fully characterized by electronic absorption spectroscopy, thin-layer cyclic voltammetry, mass spectrometry, and elemental analysis. Their solution electrochemical data show two reversible four-electron oxidation waves, indicating that these fused systems are strong pi-electron donors, which give rise to tetra- or octaradical cation species. For the metal-free phthalocyanine 5, additionally a reversible one-electron wave was found in the negative direction arising from the reduction of the macrocycle. Moreover, the tetrathiafulvalene unit acts as an efficient reductive electron-transfer quencher for the phthalocyanine emission, but upon its oxidation, an intense luminescence is switched on. 相似文献
123.
Direct numerical simulation data for the lateral velocity derivative u/y at the centreline of a fully developed turbulent channel flow provide reasonable support for Wyngaard's analysis of the error involved in measuring this quantity using parallel hot wires. Numerical data in the wall region of the channel flow also provide a useful indication of how to select the separation between the wires. Justification for this choice is obtained by comparing several measured statistics of u/y with the corresponding numerical data. 相似文献
124.
Cotton Cellulose Ageing in Sealed Vessels. Kinetic Model of Autocatalytic Depolymerization 总被引:1,自引:0,他引:1
In this paper, we propose a new kinetic model that describes the depolymerization of pure cotton cellulose, applicable to
ageing experiments in sealed vessels. By recording the pH of the salt solutions used for controlling the relative humidity
inside the vessels, we demonstrate that volatile acidic species are produced during the ageing of pure cellulose. Based on
the proposition that the acids produced must have an autocatalytic effect on the depolymerization of cellulose, we theoretically
developed equations describing the time dependence of the percentage of the broken glycosidic bonds, the folding endurance,
tensile strength, tensile energy absorption, stretch at break and the L* and b* coordinates of the CIEL*a*b* color system.
The experimentally determined values of these pure cellulose paper properties were fit into the model equations by use of
a computer statistical package. The very high values of the regression coefficients indicate that the model equations work
quite well. The experimental data and the model equations indicate that for long ageing times (up to 150 days at 80 °C), the
deterioration of the sample properties accelerates and finally brings about an abrupt breakdown of the samples. Under the
light of these findings, we believe that the useful life of the historical paper stored in archives and libraries is less
than predicted by the existing models, and steps for its preservation should be taken immediately. As an additional preservation
measure, we propose the ventilation of the storage areas so that the volatile acidic products of paper deterioration that
accelerate its ageing are removed. 相似文献
125.
Kava (Piper methysticum) dietary products have been sold worldwide for treatment of nervous anxiety, tension, and restlessness. Recent reports showed potential association of kava usage and liver injuries. This study was conducted to develop simple and reliable methodologies for the extraction and determination of 6 major kavalactones: (+)-methysticin, (+)-dihydromethysticin, (+)-kavain, (+)-dihydrokavain, yangonin, and desmethoxyyangonin. Ultrasonic extraction techniques and isocratic reversed-phase liquid chromatography (LC) were optimized for different types of samples, including capsules containing kava root extract or root powder, raw root material, tea bags, and snack bar. A suitable internal standard, 5,7-dihydroxyflavone, was used for LC calibration. Kavalactones were completely separated in 30 min using a Luna C18-2 column at 60 degrees C with an isocratic mobile phase consisting of 2-propanol-acetonitrile-water-acetic acid (16 + 16 + 68 + 0.1, v/v/v/v). Within-laboratory, intraday, and interday method variation (% relative standard deviation) for most samples extracted by methanol or methanol-water mixture were <5%. Lower levels of kavalactone contents and higher variations were observed for tea bags from water extraction or infusion as compared to methanol extraction. Labeling information of tea bags based on methanol extraction could be misleading to consumers. Analytical recoveries of snack bar fortified at 10 and 20 microg/g were >84% with RSD values <8%. Methods developed in this study offer a simple and reproducible means for analysis of kavalactones in various matrixes of dietary products. 相似文献
126.
Montserrat Alfonso Antonia Neels Helen Stoeckli-Evans 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(10):1144-1146
The new nickel(II) coordination polymer poly[diaquanickel(II)-μ-(pyrazine-2,3,5,6-tetracarboxylato)-tetraaquanickel(II)], {[{Ni(C8N2O8)(H2O)2}Ni(H2O)4]}n, has been synthesized and characterized both spectroscopically and crystallographically, by X-ray powder diffraction analysis. In this two-dimensional coordination polymer, NiII ions are bridged by pyrazine-2,3,5,6-tetracarboxylic acid, coordinating in a bis-bidentate manner, so forming one-dimensional polymeric chains. The chains are linked by a second NiII ion, via an O atom of the coordinated carboxylate group, resulting in the formation of a two-dimensional layer-like polymer. The remaining coordination sites of the two independent octahedral NiII ions are occupied by water molecules. The layers are connected via hydrogen bonds involving all six coordinated water molecules. 相似文献
127.
128.
Antonia Torres Ávila Pimenta Raimundo Braz‐Filho Piero Giuseppe Delprete Elnatan Bezerra de Souza Edilberto Rocha Silveira Mary Anne Sousa Lima 《Magnetic resonance in chemistry : MRC》2010,48(9):734-737
Two unusual monoterpene indole alkaloids, stachyoside ( 1 ) and nor‐methyl‐23‐oxo‐correantoside ( 2 ), have been isolated from the aerial parts of Psychotria stachyoides. The structural elucidation of both compounds was performed by the aid of HRESIMS, FT‐IR, and 1D‐ and 2D‐NMR techniques including COSY, HSQC, HMBC, and NOESY. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
129.
Bañuelos-Prieto J Agarrabeitia AR Garcia-Moreno I Lopez-Arbeloa I Costela A Infantes L Perez-Ojeda ME Palacios-Cuesta M Ortiz MJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(47):14094-14105
Asymmetrically substituted BODIPY analogues of the dye PM567 have been synthesised from 2-acylpyrroles and pyrroles that bear indene, fluorene or difluorene units. The type of linkage between the fluorene and the BODIPY core plays an important role in the photophysics of the BODIPY chromophore. Indeed, an aliphatic bridge gives rise to an energy-transfer process between the chromophores, whereas a vinyl spacer allows an electronic interaction between them, leading to a large red shift of the spectral bands. The laser action of the new dyes has been analysed under transversal pumping at 10 Hz repetition rate, in both liquid phase and incorporated into solid polymeric matrices. Lasing efficiencies of up to 40% were reached with high photostabilities with the laser output remaining at the initial level after 1×10(5) pump pulses in the same position of the sample. The laser action of the new dyes outperforms the laser behaviour of commercial dyes that emit in the same spectral region. The replacement of fluorene by indene quenches the fluorescence and laser emission, but allows the development of an iron cation fluorescent sensor. 相似文献
130.
Miguel Maestro Dr. Antonia Mielgo Dr. Itziar Otazo Claudio Palomo Prof. Dr. Irene Velilla 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(18):5333-5342
An anti‐selective Mannich reaction of aldehydes with N‐sulfonyl imines has been developed by using a 4‐hydroxypyrrolidine in combination with an external Brønsted acid. The catalyst design is based on three elements: the α‐substituent of the pyrrolidine, the 4‐hydroxy group, and the Brønsted acid, the combination of which is essential for high chemical and stereochemical efficiency. The reaction works with aromatic aldehyde‐derived imines, which have rarely been employed in previously reported enamine‐based anti‐Mannich reactions. Additionally, both N‐tosyl and N‐nosyl imines can be successfully used and the Mannich adducts can be easily reduced or oxidized, and after N‐deprotection the corresponding β‐amino acids and β‐amino alcohols can be obtained with good yields. The results also show that this ternary catalytic system may be practical in other enamine‐based reactions. 相似文献