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排序方式: 共有100条查询结果,搜索用时 15 毫秒
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Coen M Lindon JC Gavaghan C Holmes E Humpfer E Wilson ID Stanley PD Nicholson JK 《The Analyst》2001,126(5):548-550
High resolution 1H magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra have been obtained on typical C18 bonded silicas used in chromatographic solid-phase extraction separations. It has been shown for the first time that water molecules distributed in distinct physico-chemical environments within the chromatographic system can be detected directly using a simple 1H MAS NMR measurement. The resonances assigned to water protons in differing physico-chemical environments have distinct chemical shifts, line widths, relaxation times (T1 and T2) and also exhibit temperature dependent coalescence behaviour. This novel MAS approach may lead to a better understanding of the environments of other analytes in mixtures during such separations. 相似文献
3.
We study theoretically and experimentally the switching dynamics of a nonlinear optical bistable system that exhibits modulational instability in the vicinity of its lower limit point. We show that modulational instability induces premature upswitching and, in this way, truncates the bistable cycle. The role of the modulation instability is identified experimentally through the observation of the transient pattern formation that precedes upswitching. Our experiment illustrates the importance of cooperative behavior in practical distributed bistable systems. 相似文献
4.
Corwin KL Newbury NR Dudley JM Coen S Diddams SA Weber K Windeler RS 《Physical review letters》2003,90(11):113904
Broadband noise on supercontinuum spectra generated in microstructure fiber is shown to lead to amplitude fluctuations as large as 50% for certain input laser pulse parameters. We study this noise using both experimental measurements and numerical simulations with a generalized stochastic nonlinear Schr?dinger equation, finding good quantitative agreement over a range of input-pulse energies and chirp values. This noise is shown to arise from nonlinear amplification of two quantum noise inputs: the input-pulse shot noise and the spontaneous Raman scattering down the fiber. 相似文献
5.
Continuous-wave ultrahigh-repetition-rate pulse-train generation through modulational instability in a passive fiber cavity 总被引:1,自引:0,他引:1
Thanks to a passive cavity configuration, modulational instability in fibers is successfully observed, for the first time to our knowledge, in the continuous-wave regime. Our technique provides a new means of generating all-optically ultrahigh-repetition-rate pulse trains and opens up new possibilities for the fundamental study of modulational instability and related phenomena. 相似文献
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7.
Coen de Graaf Dr. Carmen Sousa Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(15):4550-4556
Ab initio calculations have been performed on [FeII(bpy)3]2+ (bpy=bipyridine) to establish the variation of the energy of the electronic states relevant to light‐induced excited‐state spin trapping as a function of the Fe? ligand distance. Light‐induced spin crossover takes place after excitation into the singlet metal‐to‐ligand charge‐transfer (MLCT) band. We found that the corresponding electronic states have their energy minimum in the same region as the low‐spin (LS) state and that the energy dependence of the triplet MLCT states are nearly identical to the 1MLCT states. The high‐spin (HS) state is found to cross the MLCT band near the equilibrium geometry of the MLCT states. These findings give additional support to the hypothesis of a fast singlet–triplet interconversion in the MLCT manifold, followed by a 3MLCT–HS (5T2) conversion accompanied by an elongation of the Fe? N distance. 相似文献
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9.
Magnin G. Sergent M. Coen S. Périchaud A. Phan-Tan-Luu R. 《Journal of Thermal Analysis and Calorimetry》2000,61(1):51-61
Thermal degradation of polystyrene and polyvinylchloride was studied by thermomanometric analysis. A design of experiments
was used to quantify the influence of 8 physico-chemical parameters on the responses of the analyser and on the different
types of degradation compounds.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
John D. Harvey Stuart G. Murdoch Stephane Coen Rainer Leonhardt David Mechin Gordon K. L. Wong 《Optical and Quantum Electronics》2007,39(12-13):1103-1114
Optical parametric amplification is an important nonlinear process in photonic crystal fibres driven by the small effective area and the special dispersion characteristics of these fibres. Aside from its role in supercontinuum generation, parametric amplification can lead to efficient wavelength conversion, limited primarily by the uniformity of the diameter of currently available fibres. The related Bragg scattering process can be used for both wavelength conversion and optical switching, again limited by the physical characteristics of the fibres used. 相似文献