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271.
A new spectroscopic technique is proposed as a means of determining the energy and momentum of adsorbed atoms and molecules. The method, abbreviated to ASPID (adsorption spectroscopy by polariton-induced desorption), uses surface phonon polaritons (SPPs) to desorb atoms. Because one may create nearly-monoenergetic SPPs, the binding energy range is determined directly from the spectrum of final energies. A kinematical analysis may be used to analyze adatom momenta, and hence band structures. The angular distribution of the SPP-desorbed atoms may be used to monitor adsorbed-film temperature. We provide an estimate of the SPP desorption rate, and conclude that the proposed experiment is feasible. 相似文献
272.
Anionic copolymerisation of ω-laurolactam with ε-caprolactone yields copolyesteramides with NH(CH2)11CO and O(CH2)5CO unit contents similar to those in the feeds. Over the major part of the composition range, only the amide component crystallises, showing the γ-nylon 12 form. A transition of crystalline type to that of poly(ε-caprolactone) occurs at low (ca. 20 mol%) amide-group content and with marked depression of the degree of crystallinity of the polyester component. I.R. spectroscopy indicates the co-existence of amide-ester with amide-amide hydrogen-bonding in the copolymers, and the monotonic form of the Tm vs composition curve is explained in terms of this dual bonding. It is suggested that such interactions between the sub-species may be a general feature underlying the properties of linear aliphatic copolyesteramides. 相似文献
273.
An arrangement of pseudolines is called d-stretchable if it is isomorphic to an arrangement of graphs of polynomial functions, each of degree at most d; in particular, it is 1-stretchable (classically: “stretchable”) if and only if it is isomorphic to an arrangement of lines. We show that (i) if every arrangement of n pseudolines is d-stretchable, then d ≦ cn1/2, and (ii) every arrangement of n pseudolines is d-stretchable with d = cn2. 相似文献
274.
The kinetics of the gas-phase reactions of the OH radical with (C2H5O)3PO and (CH3O)2P(S)Cl and of the reactions of NO3 radicals and O3 with (CH3O)2P(S)Cl have been studied at room temperature. Using a relative rate technique, the rate constants determined for the reactions of the OH radical with (C2H5O)3PO and (CH3O)2P(S)Cl at 296 ± 2 K and 740 torr total pressure of air were (5.53 ± 0.35) × 10?11 and (5.96 ± 0.38) × 10?11 cm3 molecule?1 s?1, respectively. Upper limits to the rate constants for the NO3 radical and O3 reactions with (CH3O)2P(S)Cl of <3 × 10?14 cm3 molecule?1 s?1 and <2 × 10?19 cm3 molecule?1 s?1, respectively, were obtained. These data are compared and discussed with previous literature data for organophosphorus compounds. 相似文献
275.
276.
The He(I) photoelectron spectrum of PF5 has been determined. Assignments for the six observed bands are suggested and comparisons with several semi-empirical molecular orbital calculations are made. Particular interest is associated with the fifth band since it exhibits vibrational fine structure. 相似文献
277.
The synthesis of 3-methylisoxazolo[4,5-b]pyrazine ( 5 ) and its 7-oxide ( 6 ) is reported. Nitration of 6 furnished the 6-nitro derivative ( 8 ) while reaction with phosphoryl chloride provided the chloro derivative ( 7 ). Efforts to functionalize the methyl group in 5 were not successful. 相似文献
278.
A new family of continuous multivariate distributions is introduced, generalizing the canonical form of the multivariate normal distribution. The well-known univariate version of this family, as developed by Box, Tiao and Lund, among others, has proven a valuable tool in Bayesian analysis and robustness studies, as well as serving as a unified model for least θ's and maximum likelihood estimates. The purpose of the family introduced here is to extend, to a degree of generality which will permit practical applications, the useful role played by the univariate family to a multidimensional setting. 相似文献
279.
For fixed p (0 ≤ p ≤ 1), let {L0, R0} = {0, 1} and X1 be a uniform random variable over {L0, R0}. With probability p let {L1, R1} = {L0, X1} or = {X1, R0} according as ; with probability 1 ? p let {L1, R1} = {X1, R0} or = {L0, X1} according as , and let X2 be a uniform random variable over {L1, R1}. For n ≥ 2, with probability p let {Ln, Rn} = {Ln ? 1, Xn} or = {Xn, Rn ? 1} according as , with probability 1 ? p let {Ln, Rn} = {Xn, Rn ? 1} or = {Ln ? 1, Xn} according as , and let Xn + 1 be a uniform random variable over {Ln, Rn}. By this iterated procedure, a random sequence {Xn}n ≥ 1 is constructed, and it is easy to see that Xn converges to a random variable Yp (say) almost surely as n → ∞. Then what is the distribution of Yp? It is shown that the Beta, (2, 2) distribution is the distribution of Y1; that is, the probability density function of Y1 is g(y) = 6y(1 ? y) I0,1(y). It is also shown that the distribution of Y0 is not a known distribution but has some interesting properties (convexity and differentiability). 相似文献
280.