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151.
152.
New semigroups of binary relations 总被引:4,自引:0,他引:4
Karen Chase 《Semigroup Forum》1979,18(1):79-82
153.
A smog chamber and modeling study of the gas phase NOx–air photooxidation of toluene and the cresols
Roger Atkinson William P. L. Carter Karen R. Darnall Arthur M. Winer James N. Pitts 《国际化学动力学杂志》1980,12(11):779-836
An experimental and modeling study of irradiated toluene–NOx–air, toluene–benzaldehyde–NOx–air, and cresol–NOx–air mixtures at part-per-million concentrations has been carried out. These mixtures were irradiated at 303 ± 1 K in a 5800-liter Teflon-lined, evacuable environmental chamber, with temperature, humidity, light intensity, spectral distribution, and the concentrations of O3, NO, NO2, toluene, PAN, formaldehyde, benzaldehyde, o-cresol, m-nitrotoluene, and methyl nitrate beingmonitored as a function of time. For the toluene and toluene–benzaldehyde–NOx–air runs a variety of initial reactant concentrations were investigated. Cresol–NOx–air runs were observed to be much less reactive in terms of O3 formation and NO to NO2 conversion rates than toluene–NOx–air runs, with the relative reactivity of the cresol isomers being in the order meta » ortho > para. The addition of benzaldehyde to toluene–NOx–air mixtures decreased the reactivity, in agreement with previous studies. Alternative mechanistic pathways for the NOx photooxidations of aromaticsystems in general are discussed, and the effects of varying these mechanistic alternatives on the model predictions for the toluene and o-cresol–NOx–air systems are examined. Fits of the calculations to most of the experimental concentration–time profiles could be obtained to within the experimental uncertainty for two of the mechanistic options considered. In both cases it is assumed that (1) O2 adds to the OH–toluene adduct ~75% of the time forming, after a further addition of O2, a C7 bicyclic peroxy radical, and (2) this C7 bicyclic peroxy radical reacts with NO ~75% of the time to ultimately form α-dicarbonyls and conjugated γ-dicarbonyls (e.g., methylglyoxal + 2-butene-1,4-dial) and ~25% of the time to form organic nitrates. The major uncertainties in the mechanisms concern (1) the structure of the bicyclicperoxy intermediate, and (2) the γ-dicarbonyl photooxidation mechanism. Good fits to the o-cresol concentration–time profiles in the toluene–NOx runs are obtained if it is assumed that o7-cresol reacts rapidly with NO3 radicals. However, it is observed that the model underpredicts nitrotoluene yields by a factor of ~10, but this is in any case a minor product. It is concluded that further experimental work will be required toadequately validate the assumptions incorporated in the aromatic photooxidation mechanisms presented here. 相似文献
154.
Two experiments compared the effect of supplying visual speech information (e.g., lipreading cues) on the ability to hear one female talker's voice in the presence of steady-state noise or a masking complex consisting of two other female voices. In the first experiment intelligibility of sentences was measured in the presence of the two types of maskers with and without perceived spatial separation of target and masker. The second study tested detection of sentences in the same experimental conditions. Results showed that visual cues provided more benefit for both recognition and detection of speech when the masker consisted of other voices (versus steady-state noise). Moreover, visual cues provided greater benefit when the target speech and masker were spatially coincident versus when they appeared to arise from different spatial locations. The data obtained here are consistent with the hypothesis that lipreading cues help to segregate a target voice from competing voices, in addition to the established benefit of supplementing masked phonetic information. 相似文献
155.
We consider a CNOT gate operation under the influence of quantum bit-flip noise and demonstrate that ac fields can change the qubit Hamiltonian in such a way that it approximately commutes with the bath coupling. Then the noise effectively acts as phase noise which improves coherence up to several orders of magnitude while the gate operation time remains unchanged. Within a high-frequency approximation, both purity and fidelity of the gate operation are studied analytically. The numerical treatment with a Bloch-Redfield master equation confirms the analytical results. 相似文献
156.
Karen Yagdjian 《Journal of Differential Equations》2004,206(1):227-252
Barros-Neto and Gelfand (Duke Math. J. 98 (3) (1999) 465; Duke Math. J. 117 (2) (2003) 561) constructed for the Tricomi operator on the plane the fundamental solutions with the supports in the regions related to the geometry of the characteristics of the Tricomi operator. We give for the Tricomi-type operator a fundamental solution relative to an arbitrary point of Rn+1 with the support in the region t?0, where the operator is hyperbolic. Our key observation is that the fundamental solution for the Tricomi-type operator can be written like an integral of the distributions generated by the fundamental solution of the Cauchy problem for the wave equation. The application of that fundamental solution to the Lp-Lq estimate for the forced Tricomi-type equation is given as well. 相似文献
157.
Karen B. Paul 《Central European Journal of Physics》2007,5(1):11-24
Fe(2 ML)/V(y ML) and interleaved Fe(2 ML)/V(y ML)/Fe(3 ML)/V(y ML) superlattice systems with spacer thicknesses, y, (4 ≤ y ≤ 17) were investigated macro-magnetically to estimate the coupling strength and the magnetoresistance in these materials,
and particularly in the antiferromagnetically coupled monolayers. The results from the magnetic and magnetoresistive measurements
indicate that adding one monolayer of Fe increases the antiferromagnetic coupling and the magnetoresistivity ratio from 0.0075
mJ/m2 at 20 K and 2 % at 10 K for Fe(2 ML)/V(y ML), to 0.05 mJ/m2 and 2.5 % for Fe(2 ML)/V(y ML)/Fe(3 ML)/V(y ML) at the same temperatures. Both systems exhibit in-plane magnetic and magnetoresistive isotropy, therefore the increase
of the conferred physical parameters is attributed mainly to the stresses at the interface as governing mechanisms over the
magnetoelastic forces.
相似文献
158.
Albert R. Matlin Karen Feit Brinton Belinda Tsao Nivaggioli 《Journal of Physical Organic Chemistry》2007,20(2):83-87
The effect of 4‐oxa substitution on the regiochemistry and rate of 5‐hexenyl radical cyclizations was investigated, as a potential model for [2 + 2] photocycloadditions of 2‐acyl‐4‐oxa‐1,5‐hexadienes. Increasing the electron density in the alkene decreases the rate of cyclization in the 4‐oxa‐hexenyl radicals, relative to the all carbon analogs, but has little effect on the regioselectivity of the cyclization. The radical model does not reproduce the high degree of 1,6 closure, observed in the [2 + 2] photocycloadditions for 4‐oxa‐1,5‐hexadiene 1a . However, the radical model does reinforce the interpretation that ground state conformational effects, engendered by substitution remote from the reacting centers have important rate consequences for cyclization reactions. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
159.
This paper describes a proportional reasoning problem set within a real‐life context and a complete analysis of one small group discussion of this problem over the course of a 90‐minute block. The seventh‐grade students' discourse is described to provide insights into typical mathematical interpretations of this problem, as well as some generalizations for other problems of this type. The interpretations provided reveal the gradual development of proportional reasoning in a local context from additive to multiplicative understandings. 相似文献
160.
As part of our survey of potential high-energy materials, we are considering molecules that have relatively high nitrogen content. Such molecules can decompose or combust to make very stable products. Here, we present calculated thermochemical properties of two molecules containing three nitrogen atoms in a ring: triaziridine
and triazirine
. Gaussian-2 and -3, CBS-APNO, and CBS-QB3 are the high-precision methods used in this study. 相似文献