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71.
R. Arletti G. Vezzalini S. Quartieri D. Ferrari M. Merlini M. Cotte 《Applied Physics A: Materials Science & Processing》2008,92(1):127-135
This work is devoted to the characterization of a suite of very rare, highly decorated and coloured glass vessels and beads
from the VII to the IV century BC. The most serious difficulty in developing this study was that any sampling – even micro-sampling
– was absolutely forbidden. As a consequence, the mineralogical and chemical nature of chromophores and opacifiers present
in these Iron Age finds were identified by means of the following synchrotron-based, strictly non-destructive, techniques:
micro X-ray fluorescence (μ-XRF), Fe K-edge micro X-ray absorption near edge spectroscopy (μ-XANES) and X-ray powder diffraction (XRPD). The μ-XRF mapping evidenced
high levels of Pb and Sb in the yellow decorations and the presence of only Sb in the white and light-blue ones. Purple and
black glass show high amounts of Mn and Fe, respectively. The XRPD analyses confirmed the presence of lead and calcium antimonates
in yellow, turquoise and white decorations. Fe K-edge μ-XANES spectra were collected in different coloured parts of the finds, thus enabling the mapping of the oxidation
state of these elements across the samples. In most of the samples iron is present in the reduced form Fe2+ in the bulk glass of the vessels, and in the oxidized form Fe3+ in the decorations, indicating that these glass artefacts were produced in at least two distinct processing steps under different
furnace conditions.
PACS 29.20.Lq; 81.80.Kf; 61.10.Ht 相似文献
72.
A Truncated Newton Method for the Solution of Large-Scale Inequality Constrained Minimization Problems 总被引:1,自引:0,他引:1
Francisco Facchinei Giampaolo Liuzzi Stefano Lucidi 《Computational Optimization and Applications》2003,25(1-3):85-122
A new active set Newton-type algorithm for the solution of inequality constrained minimization problems is proposed. The algorithm possesses the following favorable characteristics: (i) global convergence under mild assumptions; (ii) superlinear convergence of primal variables without strict complementarity; (iii) a Newton-type direction computed by means of a truncated conjugate gradient method. Preliminary computational results are reported to show viability of the approach in large scale problems having only a limited number of constraints. 相似文献
73.
De Luca L Giacomelli G Porcheddu A Salaris M Taddei M 《Journal of combinatorial chemistry》2003,5(4):465-471
The synthesis of libraries of substituted pyrazoles and isoxazoles has been developed via in situ generation of polymer-bound enaminones. The synthetic protocol makes use of commercially available aniline cellulose, a low-cost and versatile biopolymer, under very mild conditions. This new support allowed us to carry out reactions in polar solvents under both conventional heating and MW irradiation without degradation of the polymer. The reaction between cellulose-bound enaminone and hydroxylamine or hydrazines to afford the target heterocycles in high yields directly in solution is the key step. The support can be conveniently recycled. 相似文献
74.
Giovanni Meazza Giampaolo Zanardi Paolo Piccardi 《Journal of heterocyclic chemistry》1993,30(2):365-371
Trifluoromethyl-substituted pyrazoles were synthesized via 1,3-dipolar cycloaddition from sydnones 2a-j and 1-aryl-3,3,3-trifluoro-propynes 5a-f. The regioselectivity of the reaction and the spectroscopic characteristics of the products are discussed. 相似文献
75.
Barone G Duca D Silvestri A Gomez-Paloma L Riccio R Bifulco G 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(14):3240-3245
Ab initio calculations at the Hartree-Fock level with full-geometry optimization using the 6-31G(d) basis set, and GIAO (gauge including atomic orbitals) (13)C NMR chemical shifts, are presented here as a support in the study of the stereochemistry of low-polar organic compounds having an open-chain structure. Four linear stereoisomers, fragments of a natural product previously characterized by experimental (13)C NMR spectra, which possesses three stereogenic centers, 11 carbon atoms, and 38 atoms in total, were considered. Conformational searches, by empirical force-field molecular dynamics, pointed out the existence of 8-13 relevant conformers per stereoisomer. Thermochemical calculations at the ab initio level in the harmonic approximation of the vibrational modes, allowed the evaluation, at 298.15 K, of the standard Gibbs free energy of the conformers. The (13)C NMR chemical shift of a given carbon atom in each stereoisomer was considered as the average chemical shift value of the same atom in the different conformers. The averages were obtained by the Boltzmann distribution, using the relative standard free energies as weighting factors. Computed parameters related to linear correlation plots of experimental (13)C chemical shifts versus the corresponding computed average data allowed us to distinguish among the four stereoisomers. 相似文献
76.
The mass spectra of 1,2-diphenyl-pyrazolidine-3,5-dione and twenty-one 4-substituted derivatives are reported. Their fragmentation patterns have been studied by deuterium labelling, exact mass measurements, metastable studies by the defocusing technique and low energy spectra. Hydrogen rearrangements from the 4-position of the heterocycle and/or from the ß-position of the 4-substituent groups, lead to the main primary fragment ions [C12H11N2]+ (m/e 183) as shown by the metastables. The 4,4-d2 derivative shows an appreciable isotope effect even for molecular ions decomposing in the ion source. By comparison with the metastable abundances of competitive reactions, the molecular ions (m/e 252) of the 4-unsubstituted compound appear to be structurally different from the corresponding m/e 252 fragment ions formed from 4-derivatives by the loss of 4-substituent with H rearrangement. If only vinylic or aromatic hydrogen atoms are present, primary cleavage of the heterocyclic ring occurs with loss of OH·, C3O2 and C3HO2. Important rearrangements leading to elimination of C6H6N and C6H7N are typical for unsaturated substituents on position four having allylic hydrogen atoms. Fragment ions, identical to molecular ions of some compounds discussed here, are obtained by electron-impact and/or thermal decompostion of some complex compounds containing more than one 1,2-diphenyl-pyrazolidine-3,5-dione system. The [C6H5N2]+ (m/e 105) and [C6H5]+ (m/e 77) ions are common fragments of all the title compounds. Any hydrogen scrambling reactions between phenyl and heterocycle or 4-substituent groups can be excluded. 相似文献
77.
Pier Luigi Ferrarini Giuliana Biagi Oreste Livi Giampaolo Primofiore Marino Carpen 《Journal of heterocyclic chemistry》1981,18(5):1007-1010
Some 3-substituted-5,6-dihydro[1,8]naphthyrido[3,2-c][1,8]naphthyridines (V) were obtained by the condensation of 7-substituted-2,3-dihydro-1,8-naphthyridin-4-(1H)ones (IV) with 2-aminonicotinaldehyde. All of the 5,6-dihydro derivatives V were transformed into the fully aromatic compounds VI by refluxing with nitrobenzene. 相似文献
78.
Antonio Da Settimo Anna Maria Marini Giampaolo Primofiore Federico Da Settimo Daniele Bertini 《Journal of heterocyclic chemistry》1998,35(1):57-60
The synthesis of derivatives of two new heterocyclic systems, purino[8,7-b][1,3]benzothiazine and pyrido[3′,2′:5,6][1,3]thiazino[3,2-f]purine, was effected by the Ullmann reaction between 8-mercaptotheophylline or 8-bromotheophylline with the appriopriately substituted benzoic or nicotinic acid, respectively. The 8,8′-dithiobistheophylline is also reported. 相似文献
79.
Paola Caroti Carlo Ceccotti Antonio Da Settimo Fabio Palla Giampaolo Primofiore 《Journal of heterocyclic chemistry》1986,23(6):1833-1836
Reaction between 2-chloropyridine-3-carbonyl chloride and 1-alkyl-2-aminobenzimidazoles afforded the N-(1-alkylbenzimidazole-2-yl)-2-chloropyridine-3-carboxamides, which were cyclized to 5,7-dihydro-5-oxopyrido[3′,2′:5,6]pyrimido[1,2-a]benzimidazoles. The assigned structures of these hitherto unknown heterocyclic compounds were confirmed by their ir and 1H nmr spectra and chemical evidence. 相似文献
80.
Ab initio calculations were performed on the tautomers and conformers of N-hydroxyurea using a 6-31G ** basis set. The minimum-energy structures have been found and the importance of the intramolecular hydrogen bond as the stabilizing factor was pointed out. © 1996 John Wiley & Sons, Inc. 相似文献