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31.
Chemiluminescence spectra (300–800 nm) from the reactions of ozone with acetylene and allene have been obtained. These spectra show the production of electronically excited CHO, OH(2Πi, υ ? 9) and possibly C2(B3Πg, υ′ = 0 → X3Πu, υ″ = 6) from the O3 + C2H2 reaction. CH(2Δ), OH(2Σ+) and OH(2Πj, υ ? 9) emissions were identified from the O3 + C3H4 reaction in addition to the CH2O(1A″) emission previously reported. 相似文献
32.
33.
William P.L. Carter Karen R. Darnall Alan C. Lloyd Arthur M. Winer James N. Pitts 《Chemical physics letters》1976,42(1):22-27
We have calculated approximate room temperature rate constants for intramolecular hydrogen shift isomerizations of alkyl, alkoxy and alkylperoxy radical intermediates in photochemical smog and found that alkoxy radicals with δ hydrogens appear to undergo 1,5 hydrogen shifts at ambient conditions. Product distributions observed during irradiations of alkane (n-butane, n-pentane and n-hexane)NOxair systems in two quite-different ≈6000-liter environmental chambers were found to be consistent with this prediction. For example, in the n-pentaneNO xair system the observed large yields of 3-pentanone relative to 2-pentanone were consistent with room temperature rate constants which we have estimated for the corresponding hydrogen shift isomerizations. While such isomerizations have been well recognized in studies of free radicals and high temperature hydrocarbon oxidations, they are not taken into account in current kinetic mechanisms for alkane oxidation under ambient atmospheric conditions. This has implications for the construction of computer models of photo-chemical smog formation. 相似文献
34.
R.G. Smith J.C. Van Loon J.R. Knechtel J.L. Fraser A.E. Pitts A.E. Hodges 《Analytica chimica acta》1977
An inexpensive 50-ml disposable (hypodermic) syringe is used as the arsine generation vessel. The arsine is passed into a 10-cm long. 10-mm i.d. electrically heated silica tube atomizer with nitrogen carrier gas. Excess of hydrogen is burned off in a hydrogen diffusion flame at the ends of the tube. Samples containing appreciable silica are fused with KOH—MgOXXX while organic samples are digested with H2SO4—H2O2. Parameters affecting the determination of arsenic as arsine have been investigated. Collaborative results on a variety of standard reference materials agree well with literature values. The advantages of the proposed method are that it is sensitive, selective, fast, simple, inexpensive, precise and accurate. 相似文献
35.
A physical framework has been proposed which describes manifestly covariant relativistic evolution using a scalar time . Studies in electromagnetism, measurement, and the nature of time have demonstrated that in this framework, electromagnetism must be formulated in terms of -dependent fields. Such an electromagnetic theory has been developed. Gravitation must also use of -dependent fields, but many references do not take the metric's dependence on fully into account. Others differ markedly from general relativity in their formulation. In contrast, this paper outlines steps towards a -dependent classical intrinsic formulation of gravitation, patterned after general relativity, which we call parametrized general relativity (PGR). Given the existence of a preferred foliation, the Hamiltonian constraint is removed. We find that some nonmetricity in the connection is allowed, unlike in general relativity. Conditions on the allowable nonmetricity are found. Consideration of the initial value problem confirms that the metric signature should normally be O(3, 2) rather than O(4, 1). Following the lead of earlier works, we argue that concatenation (integration over ) is unnecessary for relating parametrized physics to experience, and propose an alternative to it. Finally, we compare and contrast PGR with other relevant gravitational theories. 相似文献
36.
John D. Webb A. W. Czanderna J. R. Pitts 《Journal of polymer science. Part A, Polymer chemistry》1987,25(12):3395-3403
The thermal oxidation of atactic polypropylene on CuO0.67 surfaces in air was studied using IR reflection-absorption spectroscopy. Degradative losses of primary, secondary, and tertiary alkyl hydrogens were observed. At 60 and 73°C, carboxylic acids are the primary degradation products, while at 85 and 100°C, copper carboxylate formation predominates and CuO0.67 is decomposed. The distinct change in the oxidative mechanisms between 73 and 85°C apparently is related to an irreversible thermal transition in the atactic polypropylene films, which may favor carboxylate production by increasing the permeability of the films to oxygen and water vapor. 相似文献
37.
In vivo NADH fluorescence monitoring as an assay for cellular damage in photodynamic therapy. 总被引:4,自引:0,他引:4
B W Pogue J D Pitts M A Mycek R D Sloboda C M Wilmot J F Brandsema J A O'Hara 《Photochemistry and photobiology》2001,74(6):817-824
In this study the endogenous fluorescence signal attributed to reduced nicotinamide adenine dinucleotide (NADH) has been measured in response to photodynamic therapy (PDT)-induced damage. Measurements on cells in vitro have shown that NADH fluorescence decreased relative to that of controls after treatment with a toxic dose of PDT, as measured within 30 min after treatment. Similarly, assays of cell viability indicated that mitochondrial function was reduced immediately after treatment in proportion to the dose delivered, and the proportion of this dose response did not degrade further over 24 h. Measurements in vivo were used to monitor the fluorescence emission spectrum and the excited state lifetime of NADH in PDT-treated tissue. The NADH signal was defined as the ratio of the integrated fluorescence intensity of the 450 +/- 25 nm emission band relative to the fluorescence intensity integrated over the entire 400-600 nm range of collection. Measurements in murine muscle tissue indicated a 22% reduction in the fluorescence signal immediately after treatment with verteporfin-based PDT, using a dose of 2 mg/kg injected 15 min before a 48 J/cm2 light dose at 690 nm. Control animals without photosensitizer injection had no significant change in the fluorescence signal from laser irradiation at the same doses. This signal was monotonically correlated to the deposited dose used here and could provide a direct dosimetric measure of PDT-induced cellular death in the tissue being treated. 相似文献
38.
We formulate some general network (and risk) management problems in a Bayesian context, and point out some of the essential
features. We argue and demonstrate that, when one is interested in rare events, the Bayesian and frequentist approaches can
lead to very different strategies: the former typically leads to strategies which are more conservative. We also present an
asymptotic formula for the predictive probability of ruin (for a random walk with positive drift) for large initial capital
and large number of past observations. This is a preliminary investigation which raises many interesting questions for future
research.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
39.
The non-commutative analytic Toeplitz algebra is the WOT-closed algebra generated by the left regular representation of the free semigroup onn generators. We obtain a distance formula to an arbitrary WOT-closed right ideal and thereby show that the quotient is completely isometrically isomorphic to the compression of the algebra to the orthogonal complement of the range of the ideal. This is used to obtain Nevanlinna-Pick type interpolation theoremsFirst author partially supported by an NSERC grant and a Killam Research Fellowship.Second author partially supported by an NSF grant. 相似文献
40.
Three-dimensional optical measurement of instantaneous pressure 总被引:1,自引:0,他引:1
Local perturbations in material density induced in a material by a compressional wave give rise to local perturbations in refractive index. Accurate, high-resolution, three-dimensional, optical measurements of an instantaneous refractive index perturbation in a homogeneous, optically transparent medium may be obtained from measurements of scattered optical intensity alone. The method of generalized projections allows incorporation of optical intensity measurements into an iterative algorithm for computing the phase of the interrogating optical pulse as the solution of a fixed point equation. The complex optical field amplitude, computed in this manner, is unique up to a constant unit magnitude complex coefficient. The three-dimensional refractive index distribution may be computed via the Fourier slice reconstruction algorithm from the optical phase data under the assumption of weak optical scattering. The refractive index perturbation is related to local instantaneous pressure under a linear, small-displacement model for the mechanical wave. A numerical simulation of the measurement experiment, phase recovery, and reconstruction process for a plane piston ultrasound transducer with a semicircular aperture and center frequency of 1.5 MHz is described and corresponds very well with experiment. Experimental data obtained using an 810-nm laser source are used to reconstruct the three-dimensional pressure field from two elements of a 2.5-MHz linear array. Comparison with a measurement obtained via a 500-microm needle hydrophone shows excellent agreement. 相似文献