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排序方式: 共有421条查询结果,搜索用时 15 毫秒
171.
172.
In this paper we consider an abstract Volterra integral equation in an ordered Banach space. We establish some monotonicity
properties of solutions and apply these results to their asymptotic behaviour. This is done by using the method of upper and
lower solutions. 相似文献
173.
Enzo Benedetti Francesco Posar Aldo D'Alessio Piergiorgio Vergamini Giovanni Pezzin Maria Pizzoli 《Journal of Polymer Science.Polymer Physics》1985,23(6):1187-1192
Infrared studies of the poly(vinyl chloride) (PVC)/di-n-butylphthalate (DBP) system are reported. Spectra of DBP in different solvents seem to be indicative of the ability of DBP to interact with PVC chains in the same way as with polyesters and of competitive interactions between DBP molecules and DBP with PVC. Plots of the width at half-height of the carbonyl stretching vibration, measured at 25 and at ?180°C, as a function of composition, show a sudden change of slope at about 60% PVC concentration by weight, indicating that above this polymer composition interaction between DBP and PVC dominates that between DBP molecules. This change corresponds to a “singularity” observed in the dependence of the glass transition temperature on composition. 相似文献
174.
Giancarlo Galli Emo Chiellini Michele Laus Sante A. Angeloni Daniele Caretti Enzo Fanelli Giovanni Poeti Bernard Gallot 《Liquid crystals》1994,16(1):115-125
The synthesis and characterization of a series of new polyacrylates 1, containing the azobenzene mesogen spaced from the backbone by a hexamethylene segment and substituted in the 4-position by an alkanoyl chain of variable length, together with those of the relevant precursors are reported. Optical and X-ray analyses provided evidence for the presence of a smectic A mesophase in a fairly broad range of temperature in both polymers and low molar mass compounds. In polyacrylates 1, the side-chain substituents were fully interdigitated in a smectic A1 structure. The comparison of the transition parameters of polymers 1 with those of another series of polyacrylates 7 containing the azobenzene unit substituted in the 4-position by an alkyloxy chain of variable length revealed that the replacement of an oxygen atom by a carbonyl group strongly enhanced the smectogenic character of the azobenzene group. 相似文献
175.
Massimo Bernaschi Marco Guagnelli Enzo Marinari Stefano Patarnello 《Nuclear Physics B》1991,360(2-3):283-296
We study the 3d 3-state Potts model defined on a diamond lattice (with a coordination number 4). By using finite-size scaling techniques we establish the first-order nature of the phase transition. We study local observables, tunneling events and the correlation length of the system, and we clarify the details of the pseudo-critical behavior which the system undergoes close to the transition region. 相似文献
176.
Tetrabutylammonium periodate (TBAPI) in refluxing dioxane is able to convert arylacetic acids into the corresponding nor-aldehydes in good yields. 相似文献
177.
Iengo E Zangrando E Bellini M Alessio E Prodi A Chiorboli C Scandola F 《Inorganic chemistry》2005,44(26):9752-9762
Treatment of the octahedral Ru(II) complex [trans,cis,cis-RuCl(2)(DMSO-O)(2)(CO)(2)] with an equimolar amount of 5,10-bis(3'-pyridyl)-15,20-diphenylporphyrin (3'-cis-DPyP) yielded, upon selective replacement of the DMSO ligands, the neutral 2 + 2 metallacycle 2. NMR spectroscopy provided unambiguous evidence that only one highly symmetrical species, in which the two chromophores are held in a slipped cofacial arrangement by the external Ru(II) metal fragments, exists in solution. The unprecedented geometry of 2, and of the fully zincated analogue 2a, were confirmed in the solid state by X-ray structural investigations. The spatial arrangement of the two parallel chromophores in 2, with an interplanar distance of 4.18 A and a lateral offset (center-to-center distance) of 9.82 A, is reminiscent of those of the special pair of bacteriophylls in the reaction centers and of adjacent B850 units in the LH2 light-harvesting antenna systems of photosynthetic bacteria. For comparison, the X-ray structure of the corresponding metallacycle with 4'-cis-DPyP, 1a, is also reported. In 1a, the two porphyrins have an almost perfect coplanar arrangement. The semi-zincated metallacycles 1b and 2b, in which only one of the two chromophores bears an inner zinc atom, were prepared from 1 and 2, respectively, and isolated in pure form. Detailed photophysical investigations of the above porphyrin assemblies were performed. In particular, very fast photoinduced intercomponent energy transfer processes from the zinc porphyrin to the free-base unit were detected in the semi-metalated derivatives 1b and 2b (time constants: 14 and 12 ps, respectively). 相似文献
178.
Gianni Linoli Enzo Mannucci Carlo Bergonzi 《Journal of polymer science. Part A, Polymer chemistry》1970,8(6):1481-1491
A method is described for the preparation of insoluble polymeric diazonium-salt chromogens which have a precise composition and well-defined specific reactivity and which are capable of undergoing coupling reactions to produce highly colored azo derivatives. The technique involves reaction of the acid chloride of an acrylic or methacrylic acid polymer crosslinked with divinylbenzene with an aromatic diamine, followed by diazotization of the free amino groups of the resultant aminoarylamido resin to give an insoluble diazonium salt. The aminoarylamido derivatives, the corresponding diazonium salts, and colors of the azo derivatives obtained in coupling reactions are tabulated. 相似文献
179.
Guido Viscardi Piero Savarino Ermanno Barni Rosarina Carpignano Enzo Montoneri Pierluigi Quagliotto 《Journal of heterocyclic chemistry》1992,29(4):835-839
Nitro derivatives and amines containing X-azolo[4,5-c]pyridine moieties were prepared choosing more favourable synthetic pathways. Their physical and spectroscopic data were discussed in correlation with those of previously studied systems. The heteroaromatic amines were shown to be suitable precursors for the synthesis of disperse dyes and of their cationic counterparts. 相似文献
180.
[reaction: see text] The thionium ion, generated through a cyclopropylcarbinyl-cyclobutyl ring expansion, is, for the first time, intramolecularly intercepted by activated aromatic rings to generate new versatile 2a-methyl-8b-(phenylsulfanyl-1,2a,3,8b-tetrahydro-2H-cyclobuta[c]chromenes. 相似文献