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211.
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
212.
213.
The preparation of standard specifications at national and international level on pH measurement has stimulated new experimental work on this important subject, which is reviewed here against the background of continuing international deliberations and controversy about the definition of the pH scale in terms of a single primary standard or multi-primary standards. 相似文献
214.
Arthur T. Mattick 《Journal of Quantitative Spectroscopy & Radiative Transfer》1980,24(4):323-334
Coupled radiative and convective heat transfer is investigated for an absorbing gas flowing in a finite length channel and heated by blackbody radiation directed along the flow axis. The problem is formulated in one dimension and numerical solutions are obtained for the temperature profile of the gas and for the radiation escaping the channel entrance, assuming both gray and nongray absorption spectra. Due to radiation trapping, the flowing gas is found to have substantially smaller radiation losses for a given peak gas temperature than a solid surface that is radiatively heated to this temperature. A greenhouse effect is also evident whereby radiation losses are minimized for a gas having stronger absorption at long wavelengths. 相似文献
215.
A DuPont 950 TG has been modified to permit operation at up to 30 atm, 1100°C, with corrosive atmospheres, and steam partial pressures up to 20 atm.The major areas of instrument development included: weight and temperature measurement at high pressures in a dynamic flow system; modification of a TG to accept corrosive gas atmospheres containing high partial pressures of steam; design of a pressure balanced flow system for safe introduction of corrosive gas atmospheres; design of a working steam generation system for low flows.Process studies illustrating the utility of the high presure thermobalance include the cyclic CO2-acceptor reaction for half-calcined dolomite and the cyclic H2S absorption and regeneration reaction for half-calcined dolomite 相似文献
216.
A total synthesis of the cytotoxic phytoalexin juncusol () is described. 相似文献
217.
We show for lattice U(1) gauge fields in d = 3 dimensions, that 〈exp(i∮CAdx)〉 ? exp (? const.T lnL), where C is a rectangle of dimension T × L, T ? L. This indicates quark trapping, by a potential at least as strong as Coulomb. 相似文献
218.
Arthur S. Hyman Stuart I. Yaniger Joel F. Liebman 《International journal of quantum chemistry》1978,14(6):757-766
From the general formalism of elastic x-ray scattering and a few meaningful assumptions we have shown that for an atom, ∫ρ2dτ is an experimentally measurable quantity related to the intensity scattered by an element. We have labeled this quantity (p), the “average electron density.” If ψ obeys the virial theorem, within the Thomas–Fermi approximation we show (within a multiplicative constant) that 〈ρ〉 is a lower bound to (∑ ionization potentials )3/2. Thus, the scattered intensity of x rays is related quantitatively to the energy of the scattering atoms. Inequalities have been developed to express these relationships and have been confirmed for the more exact Hartree–Fock wave functions. 相似文献
219.
Sarah?Cassell Arthur?KavanaughEmail author 《Journal of immune based therapies and vaccines》2005,3(1):6
Psoriatic arthritis (PsA) is a chronic inflammatory arthropathy characterized by the association of arthritis and psoriasis.
PsA runs a variable course, from mild synovitis to severe, progressive, erosive arthropathy. The pathogenesis of PsA involves
alteration in the components of the immune response, although the exact cause of PsA is unknown. A number of patients with
severe peripheral arthritis fail to respond to standard conventional therapy. Advances in biotechnology and in our understanding
of the immunopathogenesis of PsA have led to great interest and progress in regards to biologic treatments for PsA. Notable
success achieved with recently introduced biologic therapies has paved the way for further research and develpoment of additional
therapies that should improve outcomes for affected patients. 相似文献
220.
This study investigates in detail the freezing events during cooling of solutions of various size classes of antifreeze glycoproteins. Differential scanning calorimetry and nanolitre osmometry were used to observe ice growth at temperatures within the hysteresis gap between the melting point and non-equilibrium freezing point (hysteresis freezing point) of solutions of the various sized antifreeze glycoproteins (AFGPs). The ice growth within the hysteresis gap is presumably due to both the expression of primary or near primary prism planes and also some growth at the basal plane. The binding of the AFGPs to the ice causes a particular ice crystal morphology. With the smaller AFGPs, substantial microscopic ice growth was observed in the form of a hexagonal bipyramids within the hysteresis gap. 相似文献