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Sanchez-sanz M; Blyth MG 《The Quarterly Journal of Mechanics and Applied Mathematics》2007,60(2):125-138
Unsteady, axisymmetric stagnation flow about a circular cylinderis examined when the far-field flow is a periodic function oftime with a fixed time average and an oscillatory part of prescribedamplitude and frequency. Solutions are computed for arbitraryvalues of the Reynolds number, quantifying the effects of surfacecurvature, and a frequency parameter based on the period ofthe far-field flow. It is found that solutions remain regularand periodic provided that the far-field amplitude lies belowa critical value. Above this value, solutions terminate in afinite-time singularity. The blow-up time is delayed by increasingthe curvature of the surface. These results are corroboratedby asymptotic predictions valid in the limits of small and largeamplitude and frequency. For large Reynolds number, the problemreduces to the two-dimensional stagnation-point flow againsta plane wall studied by previous authors. 相似文献
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S -nitrosothiols have many biological activities and may act as nitric oxide (NO) carriers and donors, prolonging NO half-life in vivo. In spite of their great potential as therapeutic agents, most S -nitrosothiols are too unstable to isolate. We have shown that the S -nitroso adduct of N -acetylcysteine (SNAC) can be synthesized directly in aqueous and polyethylene glycol (PEG) 400 matrix by using a reactive gaseous (NO/O2 ) mixture. Spectral monitoring of the S–N bond cleavage showed that SNAC, synthesized by this method, is relatively stable in nonbuf-fered aqueous solution at 25°C in the dark and that its stability is greatly increased in PEG matrix, resulting in a 28-fold decrease in its initial rate of thermal decomposition. Irradiation with UV light (λ= 333 nm) accelerated the rate of decomposition of SNAC to NO in both matrices, indicating that SNAC may find use for the photogeneration of NO. The quantum yield for SNAC decomposition decreased from 0.65 ± 0.15 in aqueous solution to 0.047 ± 0.005 in PEG 400 matrix. This increased stability in PEG matrix was assigned to a cage effect promoted by the PEG microenvironment that increases the rate of geminated radical pair recombination in the homolytic S–N bond cleavage process. This effect allowed for the storage of SNAC in PEG at −20°C in the dark for more than 10 weeks with negligible decomposition. Such stabilization may represent a viable option for the synthesis, storage and handling of S -nitrosothiol solutions for biomedical applications. 相似文献
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Watson MD Debije MG Warman JM Müllen K 《Journal of the American Chemical Society》2004,126(3):766-771
A remarkable, regiospecific hydrogenation zips around the approximately 4 nm perimeter of hexa-peri-hexabenzocoronenes (HBC) adding 18 hydrogen atoms, leading to the first peralkylated coronenes, in quantitative yields in some cases. Increasing steric bulk of side chains was found to hinder the reaction, while unsubstituted HBC could be converted to a modest extent despite its vanishing solubility. The structures of the novel coronenes are unequivocally confirmed by MALDI-TOF, 1H, 13C, and heteronuclear correlation NMR, and UV-vis absorption spectroscopy. The puckered-ring periphery of these discotics does not prohibit self-assembly to columnar structures in a fashion similar to that of the planar precursors, as determined from wide-angle X-ray diffraction, but decreases the isotropization temperature by approximately 300 degrees C relative to the latter. Branching in the alkyl chains frustrates nucleation from the melt, resulting in clear polymorphism depending on the thermal treatment. Nonetheless, preliminary measurements indicate high charge-carrier mobilities and lifetimes within the bulk material, on the same order as those previously found for HBCs. 相似文献
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Augustinus J. J. Kragt Roel C. G. M. Loonen Dirk J. Broer Michael G. Debije Albert P. H. J. Schenning 《Journal of polymer science. Part A, Polymer chemistry》2021,59(12):1278-1284
'Smart' windows which reversibly increase their reflectivity upon heating are attracting considerable attention as devices for maintaining comfortable indoor environmental conditions. In this work, twisted nematic semi-interpenetrating liquid crystal networks which lose their order upon heating are sandwiched between reflective linear polarizers. This 'smart' window reversibly decreases its transmission from about 50–10% over a wavelength range between 400 and 1100 nm upon heating, resulting in the window becoming darker and reflecting more light. This 'smart' window is potentially interesting for energy saving window applications where variation between privacy and visible light transparency states is required. 相似文献
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马丽娜 《纯粹数学与应用数学》2007,23(4):549-555
通过构造两个非负鞅证明了一个强极限定理,然后把它应用到本文所定义的广义Bethe树上的奇偶马尔可夫链场上,从而获得了此马氏链场上的一类强极限定理. 相似文献
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Dario Cambi Jeroen Dobbelaar Paola Riente Jochen Vanderspikken Chong Shen Peter H. Seeberger Kerry Gilmore Michael G. Debije Timothy Noël 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(40):14512-14516
The sun is the most sustainable light source available on our planet, therefore the direct use of sunlight for photochemistry is extremely appealing. Demonstrated here, for the first time, is that a diverse set of photon‐driven transformations can be efficiently powered by solar irradiation with the use of solvent‐resistant and cheap luminescent solar concentrator based photomicroreactors. Blue, green, and red reactors can accommodate both homogeneous and multiphase reaction conditions, including photochemical oxidations, photocatalytic trifluoromethylation chemistry, and metallaphotoredox transformations, thus spanning applications over the entire visible‐light spectrum. To further illustrate the efficacy of these novel solar reactors, medicinally relevant molecules, such as ascaridole and an intermediate of artemisinin, were prepared as well. 相似文献
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Michael G. Debije Michael T. Milano William A. Bernhard 《Angewandte Chemie (International ed. in English)》1999,38(18):2752-2756
The yields of radicals trapped on DNA, measured by EPR spectroscopy of oligodeoxyribonucleotide crystals (the EPR spectrum of a single crystal of d(CCCTAGGG) is shown), are found to be very high (0.7 μmol J−1) and insensitive to long-range (>106 base pairs) versus short-range stacking (8 base pairs) of the bases. These observations are evidence that DNA at 4 K has the properties of an insulator and argue against DNA acting as a “molecular wire”. 相似文献