排序方式: 共有108条查询结果,搜索用时 281 毫秒
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We study the effect of large-scale spectral forcing on the scale-dependent anisotropy of the velocity field in direct numerical simulations of homogeneous turbulence. ABC-type forcing and helical or non-helical Euler-type forcing are considered. We propose a scale-dependent characterisation of anisotropy based on a modal decomposition of the two-point velocity tensor spectrum. This produces direction-dependent spectra of energy, helicity and polarisation. We examine the conditions that allow anisotropy to develop in the small scales due to forcing and we show that the theoretically expected isotropy is not exactly obtained, even in the smallest scales, for ABC and helical Euler forcings. When adding rotation, the anisotropy level in ABC-forced simulations is similar to that of lower Rossby number Euler-forced runs. Moreover, even at low rotation rate, the natural anisotropy induced by the Coriolis force is visible at all scales, and two distinct wavenumber ranges appear from our fine-grained characterisation, not separated by the Zeman scale but by a scale where rotation and dissipation are balanced. 相似文献
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Hongming Yi Weidong Chen Aurore Vicet Zhensong Cao Xiaoming Gao Tong Nguyen-ba Mohammad Jahjah Yves Rouillard Lars Nähle Marc Fischer 《Applied physics. B, Lasers and optics》2014,116(2):423-428
This paper reports on the development of a gas sensor involving a newly available 3.38-μm distributed feedback laser in combination with a novel T-shape microresonator-based quartz-enhanced photoacoustic spectroscopy (T-mR QEPAS), capable of simultaneous monitoring of multi-species (such as CH4, H2CO, HCl, C2H4) using the same QEPAS spectrophone. As a first demonstration, monitoring of ambient methane (CH4) was achieved at atmospheric pressure with a 1σ detection limit of 400 ppbv (parts per billion by volume) in an integration time of 10 s and a water vapor concentration of 1.15 vol% (11,500 ppm) in the atmosphere, which is very suitable for field measurement of CH4 emission. 相似文献
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We observe an insulator-to-metal transition in crystalline silicon doped with sulfur to nonequilibrium concentrations using ion implantation followed by pulsed-laser melting and rapid resolidification. This insulator-to-metal transition is due to a dopant known to produce only deep levels at equilibrium concentrations. Temperature-dependent conductivity and Hall effect measurements for temperatures T>1.7 K both indicate that a transition from insulating to metallic conduction occurs at a sulfur concentration between 1.8 and 4.3×10(20) cm(-3). Conduction in insulating samples is consistent with variable-range hopping with a Coulomb gap. The capacity for deep states to effect metallic conduction by delocalization is the only known route to bulk intermediate band photovoltaics in silicon. 相似文献
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Aurore Loudet 《Tetrahedron》2008,64(17):3642-3654
Fluorescent molecules that emit in the near infrared are potentially useful as probes for biotechnology. A relatively under-explored design for probes of this type are the aza-BODIPY dyes; this study was performed to enhance our understanding of these materials and ways in which they may be used in dye cassette systems. Thus, the aza-BODIPY dyes 1a-g were prepared. An advanced intermediate toward an eighth compound in the series, 6h, was made but it could not be complexed with boron effectively to give 1h. Spectroscopic properties of these compounds were recorded, and correlations between substituent effects, UV absorbance, fluorescence emissions, and quantum yields were made. Compound 1a was coupled with a fluorescein-alkyne derivative to give the energy transfer cassettes 2 and 3. Both these compounds gave poor energy transfer and the possible reasons for this were discussed. 相似文献
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Characterization of dehydroascorbate‐mediated modification of glutaredoxin by mass spectrometry 下载免费PDF全文
Aurore Flandrin Sebastien Allouche Yoann Rolland François‐Olivier McDuff J. Richard Wagner Klaus Klarskov 《Journal of mass spectrometry : JMS》2015,50(12):1358-1366
Ascorbate is as a potent antioxidant in vivo protecting the organism against oxidative stress. In this process, ascorbate is oxidized in two steps to dehydroascorbate (DHA), which if not efficiently reduced back to ascorbate decomposes irreversibly to a complex mixture of products. We demonstrate that a component of this mixture specifically reacts with the thiol group of cysteine residues at physiological pH to give a protein adduct involving the addition of a 5‐carbon fragment of DHA (+112 Da). Incubations of glutaredoxin‐1 expressed in Escherichia coli and dehydroascorbate revealed abundant adducts of +112, +224 and +336 Da due to the addition of one, two and three conjugation products of DHA, respectively. ESI–MS of carbamidomethylated glutaredoxin‐1 before incubation with DHA, deuterium exchange together with tandem mass spectrometry analysis and LC–ESIMS/MS of modified peptides confirmed structure and sites of modification in the protein. Modification of protein thiols by a DHA‐derived product can be involved in oxidative stress‐mediated cellular toxicity. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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Synthesis of Enantioenriched 5,6‐Dihydrophenanthridine Derivatives through retro‐Carbopalladation of Chiral o‐Bromobenzylamines 下载免费PDF全文
Dr. Juntao Ye Aurore Limouni Sonia Zaichuk Prof. Dr. Mark Lautens 《Angewandte Chemie (International ed. in English)》2015,54(10):3116-3120
Retro‐carbopalladation of aldimines in the presence of a suitable β‐hydrogen atom has been observed in the Pd‐catalyzed homocoupling reactions of o‐bromobenzylamines, providing an expeditious synthetic route to 5,6‐dihydrophenanthridine derivatives. Furthermore, a highly enantioselective synthesis of 6‐aryl‐substituted 5,6‐dihydrophenanthridines was achieved in a one‐pot manner by taking advantage of Rh and Pd catalysis. 相似文献
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P. Kluczynski M. Jahjah L. N?hle O. Axner S. Belahsene M. Fischer J. Koeth Y. Rouillard J. Westberg A. Vicet S. Lundqvist 《Applied physics. B, Lasers and optics》2011,105(2):427-434
Using recently developed GaInAsSb/AlGaInAsSb DFB lasers, tunable diode laser spectroscopy (TDLS) has been extended into the 3-??m wavelength region for the detection of acetylene impurities in hydrocarbon compounds encountered in ethylene manufacturing. Measurements of acetylene in pure polymer grade ethylene and in a gas mixture of ethylene and ethane typical of the process stream around a hydrogenation reactor have been performed. Using a procedure incorporating subtraction of a hydrocarbon background spectrum a detection limit of 5?ppb?m was achieved under ordinary laboratory conditions. Under forced temperature cycling conditions, the detection limit deteriorated to 180 ppb?m, due to temperature drift caused by optical interferences generated by reflections in the laser TO8 can. 相似文献
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Razafindralambo H Richel A Wathelet B Blecker C Wathelet JP Brasseur R Lins L Miñones J Paquot M 《Physical chemistry chemical physics : PCCP》2011,13(33):15291-15298
By screening uronic acid-based surfactant interfacial properties, the effect of the hydroxyl group stereochemistry (OH-4) on the conformation of bicatenary (disubstituted) derivatives at the air-water interface has been evidenced by experimental and computational approaches. Physical and optical properties of a monolayer characterized by Langmuir film balance, Brewster angle microscopy, and ellipsometry at 20 °C reveal that the derivative of glucuronate (C(14/14)-GlcA) forms a more expanded monolayer, and shows a transition state under compression, in the opposite to that of galacturonate (C(14/14)-GalA). Both films are very mechanically resistant (compression modulus > 300 mN m(-1)) and stable (collapse pressure exceeding 60 mN m(-1)), while that of C(14/14)-GalA exhibits a very high compression modulus up to 600 mN m(-1) like films in the solid state. Computational approaches provide single and assembly molecular models that corroborate the molecule expansion degree and interactions data from experimental results. Differences in the molecular conformation and film behaviours of uronic acid bicatenary derivatives at the air-water interface are attributed to the intra-H-bonding formation, which is more favourable with an OH-4 in the axial (C(14/14)-GalA) than in the equatorial position (C(14/14)-GlcA). 相似文献