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A simple mass-spring system is submitted to a constant force in addition to a periodic perturbation of rectangular wave shape. It has been obtained in a previous study that the range of the period-amplitude plane of this perturbation, where the trajectories are sliding with no loss of contact, is divided into two parts, one in which there exist infinitely many equilibrium states and no periodic solutions, and another one where there exist periodic solutions and no equilibrium states. The present work focuses on the transition between these two parts. All along the transition line, there exists a single equilibrium state. Initial data out of equilibrium lead either to a periodic trajectory, or to a trajectory, which tends to the equilibrium or to a periodic solution, either in finite time or at infinity. 相似文献
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Dwight W. Chasar Timothy M. Pratt J. P. Shockcor 《Phosphorus, sulfur, and silicon and the related elements》2013,188(2):183-186
Abstract The reaction of variously substituted diaryl sulfoxides with anhydrous HCl in chloroform was examined. The products ranged from the corresponding sulfides to mono- and dichlorinated sulfides and sulfoxides. The same reaction in the presence of phenol afforded primarily the corresponding sulfides accompanied by o- and p-chlorophenol. The latter reaction is an efficient means for deoxygenating diaryl sulfoxides. The mechanism of the reaction and the nature of the chlorinating species are discussed. 相似文献
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Claire L. Phillips Nick Nickerson David Risk Zachary E. Kayler Chris Andersen Alan Mix Barbara J. Bond 《Rapid communications in mass spectrometry : RCM》2010,24(9):1271-1280
The carbon isotopic composition (δ13C) of recently assimilated plant carbon is known to depend on water‐stress, caused either by low soil moisture or by low atmospheric humidity. Air humidity has also been shown to correlate with the δ13C of soil respiration, which suggests indirectly that recently fixed photosynthates comprise a substantial component of substrates consumed by soil respiration. However, there are other reasons why the δ13CO2 of soil efflux may change with moisture conditions, which have not received as much attention. Using a combination of greenhouse experiments and modeling, we examined whether moisture can cause changes in fractionation associated with (1) non‐steady‐state soil CO2 transport, and (2) heterotrophic soil‐respired δ13CO2. In a first experiment, we examined the effects of soil moisture on total respired δ13CO2 by growing Douglas fir seedlings under high and low soil moisture conditions. The measured δ13C of soil respiration was 4.7‰ more enriched in the low‐moisture treatment; however, subsequent investigation with an isotopologue‐based gas diffusion model suggested that this result was probably influenced by gas transport effects. A second experiment examined the heterotrophic component of soil respiration by incubating plant‐free soils, and showed no change in microbial‐respired δ13CO2 across a large moisture range. Our results do not rule out the potential influence of recent photosynthates on soil‐respired δ13CO2, but they indicate that the expected impacts of photosynthetic discrimination may be similar in direction and magnitude to those from gas transport‐related fractionation. Gas transport‐related fractionation may operate as an alternative or an additional factor to photosynthetic discrimination to explain moisture‐related variation in soil‐respired δ13CO2. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
966.
We review what we have learned about the scattering of electrons by the interfaces between two different metals (M1/M2) in the current-perpendicular-to-plane (CPP) geometry. In this geometry, the intrinsic quantity is the specific resistance, AR, the product of the area through which the CPP current flows times the CPP resistance. We describe results for both non-magnetic/non-magnetic (N1/N2) and ferromagnetic/non-magnetic (F/N) pairs. We focus especially upon cases where M1/M2 are lattice matched (i.e., have the same crystal structure and the same lattice parameters to within ∼1%), because in these cases no-free-parameter calculations of 2AR agree surprisingly well with measured values. But we also list and briefly discuss cases where M1/M2 are not lattice matched, either having different crystal structures, or lattice parameters that differ by several percent. The published calculations of 2AR in these latter cases do not agree so well with measured values. 相似文献
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Nick M. Marinov 《国际化学动力学杂志》1999,31(3):183-220
A detailed chemical kinetic model for ethanol oxidation has been developed and validated against a variety of experimental data sets. Laminar flame speed data (obtained from a constant volume bomb and counterflow twin‐flame), ignition delay data behind a reflected shock wave, and ethanol oxidation product profiles from a jet‐stirred and turbulent flow reactor were used in this computational study. Good agreement was found in modeling of the data sets obtained from the five different experimental systems. The computational results show that high temperature ethanol oxidation exhibits strong sensitivity to the fall‐off kinetics of ethanol decomposition, branching ratio selection for C2H5OH + OH ↔ Products, and reactions involving the hydroperoxyl (HO2) radical. The multichanneled ethanol decomposition process is analyzed by RRKM/Master Equation theory, and the results are compared with those obtained from earlier studies. The ten‐parameter Troe form is used to define the C2H5OH(+M) ↔ CH3 + CH2OH(+M) rate expression as k∞ = 5.94E23 T−1.68 exp(−45880 K/T) (s−1) ko = 2.88E85 T−18.9 exp(−55317 K/T) (cm3/mol/sec) Fcent = 0.5 exp(−T/200 K) + 0.5 exp(−T/890 K) + exp(−4600 K/T) and the C2H5OH(+M) ↔ C2H4 + H2O(+M) rate expression as k∞ = 2.79E13 T0.09 exp(−33284 K/T) (s−1) ko = 2.57E83 T−18.85 exp(−43509 K/T) (cm3/mol/sec) F cent = 0.3 exp(−T/350 K) + 0.7 exp(−T/800 K) + exp(−3800 K/T) with an applied energy transfer per collision value of <ΔEdown> = 500 cm−1. An empirical branching ratio estimation procedure is presented which determines the temperature dependent branching ratios of the three distinct sites of hydrogen abstraction from ethanol. The calculated branching ratios for C2H5OH + OH, C2H5OH + O, C2H5OH + H, and C2H5OH + CH3 are compared to experimental data. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 183–220, 1999 相似文献