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381.
This tutorial review describes the use of variable temperature infrared spectroscopy of adsorbed species (VTIR), a recent method for studying the thermodynamics of weak solid-gas interactions. Examples show how a fundamental relationship of thermodynamics (the van't Hoff equation, used long since in several fields of physical chemistry) can describe equilibrium processes at the solid-gas interface. The VTIR method is fully exploited by measuring absorbance of an IR band, temperature and pressure over a wide temperature range: an estimation of the interaction energy is, however, possible even ignoring the equilibrium pressure. Precise thermodynamic characterization of solid-gas interactions is required in several fields: on the applied side, gas sensing, separation and storage, which involve such areas as work-place security, air pollution control and the energy sector; regarding fundamental knowledge, weak solid-gas interactions are relevant to a number of fields, including hydrogen bonding, coordination chemistry and surface phenomena in a broad sense.Infrared (IR) spectroscopy of (gas) molecules adsorbed on a solid is frequently used to characterize both, the adsorbed species and the adsorbing centres at the solid surface. The potential of the technique can be greatly enhanced by obtaining IR spectra over a temperature range, and simultaneously measuring IR absorbance, temperature and equilibrium pressure. When this is done, variable temperature infrared (VTIR) spectroscopy can be used not only for a more detailed surface characterization, but also for precise studies on the thermodynamics of solid-gas interactions. Furthermore, when weak interactions are concerned, the technique shows favourable features compared to adsorption calorimetry, or to other classical methods. The potential of the VTIR method is highlighted by reviewing recently reported studies on dihydrogen, dinitrogen and carbon monoxide adsorption on zeolites. To facilitate understanding, an outline of the basis of the method is also given, together with an appraisal of the critical points involved in its practical use. 相似文献
382.
Mauro Aglietto Luca Cioni Giacomo Ruggeri Elisa Taburoni Edoardo Tomei 《Journal of polymer science. Part A, Polymer chemistry》1986,24(6):1337-1349
The preparation of 2-methoxy-5-t-butylphenyl vinyl ketone (MeOBVK), 2-hydroxy-5-t-butylphenyl vinyl ketone (HOBVK), and 2-methoxy-5-isooctylphenyl vinyl ketone (MeOOVK) is reported. These compounds can be considered as precursors of polymerizable derivatives of polyoxyethylated alkylphenols—a very important class of nonionic surface active compounds. The homopolymerization and copolymerization of MeOBVK, HOBVK, and MeOOVK with butylacrylate (BA), (–) menthylacrylate [(–)MtA], styrene (STY), and vinylacetate (VA) by free radical initiators, both in solution and emulsion, have been investigated. Copolymer formation has been demonstrated by fractionation and by the presence of induced optical activity in the electronic transitions of the achiral MeOBVK and HOBVK units in copolymers with the optically active comonomer (—)MtA. MeOBVK, HOBVK and MeOOVK give substantially random copolymers with STY, BA, or VA under all conditions investigated, and always show larger reactivity; thus, depending on feed composition, sequences of the vinyl ketone units can be expected in the macromolecules. 相似文献
383.
The separation of the major flavanone-7-O-glycoside constituents of Citrus was carried out by isocratic reversed phase capillary electrochromatography using a 75 microm i.d. silica fused column packed with 5 microm ODS silica gel. In comparison to HPLC mode, capillary electrochromatography resolution of flavanone glycosides was obtained with a high selectivity factor. Optimum separation conditions were found using a mixture of ammonium formate (pH 2.5)--acetonitrile (8:2, v/v) as the mobile phase by the short-end injection mode. Under these conditions all the investigated flavanones were baseline-resolved within short analysis time (i.e. between 5 and 10 min). A study, evaluating the intra- and inter-day repeatability as well as limit of detection and method linearity, was developed in accordance with the analytical procedures for method validation. The developed method was applied for the quantitative analysis of flavanone glycosides in commercial fruit juices (sweet orange, lemon and grapefruit). 相似文献
384.
The kinetic method described for the determination of a single alcohol (? 5 X 10-4 M), or of a binary mixture of alcohols in aqueous solution is based on fast oxidation by silver(II), monitored spectrophotometrically by using a stopped-flow technique. Mixtures of alcohols having rate constants differing by a factor of ?3 can be resolved. The lower limit of determination is ca. 5 × 10-4 M. 相似文献
385.
386.
Here we prove the following result on Weierstrass multiple points.
Theorem:Fix integers k, g with k≥5 and g>4k. Then there exist a genus g, Riemann surface X and k points P
1, …,P
k
of X such that for all integers b
1≥…≥b
k
≥0we have:
.
By Riemann-Roch the value given is the lowest one compatible withk, g and the inequalityh
0(X,O
X
(P
1+…+P
k
))≥2. Hence this theorem means that (P
1, …,P
k
) is ak-ple Weierstrass set with the lowest weight possible compatible with the integersk andg. Using similar tools we prove a theorem on the non-gap sequence of a Weierstrass point onm-gonal curves and study theg
d
r
’s on a generalk-sheeted covering of an irrational curve. Then we introduce and study a class of vector bundles on coverings of elliptic curves. 相似文献
387.
Summary The kinetics and mechanism of oxidation of 1,4-dihydroxybenzene (H2Q), 2,5-dihydroxybenzenesulphonic acid (H2SQ) and 4,5-dihydroxy-1,3-benzenedisulphonic acid (H2T) to the correspondingortho orPara-quinones by ethylenediaminetetraacetatomanganate (III) has been investigated over the 2.5–6.0 pH range, at 20.0° by the stopped-flow technique. Complex behaviour is observed for H2Q due to the superposition of the precursor complex formation and the redox act, while at higher pH's these reactions separate. For the other substrates, a single second order step (first order in each reactant) was present whose rate showed different pH dependences. All these features are discussed with reference to the reduction potential of the substrates, their acidity and coordinating ability. 相似文献
388.
Edoardo Scarpetta Mezhlum A. Sumbatyan 《Journal of Mathematical Analysis and Applications》2008,337(1):576-593
In the context of wave propagation in damaged composite elastic media, an analytical approach is developed to study the normal penetration of a longitudinal wave into a periodic array of interface thin defects (cracks) between two different materials. The problem is reduced to some integral equations which hold over the opening between adjacent cracks and are independent on frequency. By means of an original procedure, such equations are solved and some related integrals are calculated, so that an explicit analytical representation can be provided for the relevant scattering parameters. Finally, several graphs are set up which reflect the peculiarities of the structure; an excellent agreement is observed—in the concerned (one-mode) regime of propagation—between the obtained formulas and results from a full-numerical treatment of the problem. 相似文献
389.
390.
Edoardo Vesentini 《Advances in Mathematics》2005,191(2):423-445
The main purpose of this paper is to investigate extensions of the Banach-Stone theorem and of the Holsztynski theorem to some locally multiplicatively convex associative algebras. The proofs are based on a generalization of a theorem, due to A. Gleason, J.-P. Kahane and W. Zelazko, characterizing continuous characters of a unital associative Banach algebra among all its linear forms. 相似文献