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81.
Robert A. Burrow David H. Farrar Alan J. Lough Márcia R. Siqueira Fatima Squizani 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(8):e357-e358
The crystal structure of the title compound, C6H7O2P, shows continuous hydrogen-bonding chains in the x direction, with a P—O⋯O=P distance of 2.513 (3) Å. 相似文献
82.
Volker Bach Walter de Siqueira Pedra Marco Merkli Israel Michael Sigal 《Journal of statistical physics》2014,155(6):1271-1298
We consider a finite-dimensional quantum system coupled to a thermal reservoir and subject to a time-periodic, energy conserving forcing. We show that, if a certain dynamical decoupling condition is fulfilled, then the periodic forcing counteracts the decoherence induced by the reservoir: for small system–reservoir coupling $\lambda $ and small forcing period $T$ , the system dynamics is approximated by an energy conserving and non-dissipative dynamics, which preserves coherences. For times up to order $(\lambda T)^{-1}$ , the difference between the true and approximated dynamics is of size $\lambda +T$ . Our approach is rigorous and combines Floquet and spectral deformation theory. We illustrate our results on the spin-fermion model and recover previously known, heuristically obtained results. 相似文献
83.
Antônio C. Doriguetto Rodrigo S. Corrêa Fernanda A. Siqueira Luiz F. Silva Jr. Javier Ellena 《Structural chemistry》2009,20(5):795-800
This paper presents the structural characterization of the indan derivative (±)-1-trans-3-(3,4-dichlorophenyl)-2,3-dihydro-1H-indene-1-carboxamide, which was unambiguously determined by X-ray diffraction (XRD) to be a racemate (R/S: 50/50) crystallizing in an achiral crystal structure (P21/c, a = 9.3180(1) Å, b = 7.9070(2) Å, c = 19.7550(4) Å, β = 103.250(1)°, V = 1416.75(5) Å3 and Z = 4). The diastereomers are related by the inversion symmetry and linked by H bond forming a dimer. The crystal packing is stabilized by hydrogen bonds, including the classical one responsible for the formation of centrosymmetric dimers, and non-classical ones involving C–H···O and C–H···π-aryl interactions. The intra and intermolecular geometry of the title compound is compared to the (±)-1-trans-3-(3,4-dichlorophenyl)-2,3-dihydro-1H-indene-1-carboxylic acid one, which also present an achiral crystal structure from racemates (R/S: 50/50). The two indan derivatives crystallize in a very similar unit cell. 相似文献
84.
B. Ambrozini P. R. Dametto A. B. Siqueira C. T. Carvalho M. Ionashiro 《Journal of Thermal Analysis and Calorimetry》2009,97(2):761-764
Solid state Ln–L compounds, where Ln stands for light trivalent lanthanides (L–Gd) and L is tartrate, have been synthesized.
Thermogravimetry and differential thermal analysis (TG/DTA), differential scanning calorimetry (DSC), X-ray powder diffractometry,
elemental analysis and complexometry were used to characterize and to study the thermal behaviour of these compounds. The
results led to information about the composition, dehydration and thermal decomposition of the isolated compounds. 相似文献
85.
Stereoselective syntheses of enantiomerically enriched trihydroxy pyrrolizidine and indolizidines were accomplished from a common chiral endocyclic enecarbamate. The synthetic strategy features an efficient [2+2] cycloaddition of ketenes to the endocyclic enecarbamate and a highly regioselective Baeyer-Villiger oxidation of the intermediate azabicyclic-cyclobutanones. These new heterocycles are compounds structurally related to the alexines. 相似文献
86.
Bretanha LC Teixeira VE Ritter M Siqueira GM Cunico W Pereira CM Freitag RA 《Ultrasonics sonochemistry》2011,18(3):704-707
The alternative synthesis of 12 1,2,4-oxadiazoles using ultrasound irradiation from trichloroacetoamidoxime and acyl chlorides is reported. Seven of them are novel compounds. The 3-trichloromethyl-5alkyl(aryl)-1,2,4-oxadiazoles have been synthesised in better yields and shorter reaction times compared to the conventional method. This protocol can be applicable for preparation of 1,2,4-oxadiazoles containing aryl or alkyl groups attached at their C-5 side-chain. 相似文献
87.
E.M. de Sousa Luz A.F. Siqueira U.M.S. Costa M.L. Lyra 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):115-118
The recent improvements on the technology for developing high-quality thin magnetic films has renewed the interest in the
study of surface effects in both static and dynamic magnetic responses. In this work, we use a Monte-Carlo algorithm with
Metropolis dynamics together with a spreading of damage technique to study the interplay between the effects of finite thickness
and surface ordering field in thin ferromagnetic Ising (S=1/2) films. We calculate, near the bulk critical temperature and several values of the surface field, the dependence on the
film thickness of the average magnetization M and Hamming distance D. We employ a finite size scaling analysis to show that both obey an effective one-parameter scaling but exhibit distinct
characteristic surface fields. At their corresponding characteristic surface fields both M and D become roughly thickness independent and we estimate the critical exponent characterizing the behavior of the typical scaling
lengths.
Received 29 March 1999 and Received in final form 21 April 1999 相似文献
88.
Marcos A. P. Martins Geonir M. Siqueira Giovani P. Bastos Helio G. Bonacorso Nilo Zanatta 《Journal of heterocyclic chemistry》1996,33(6):1619-1622
β-Aryl-β-methoxyvinyl trihalomethyl ketones 1a-g, 2a-g [aryl = p-YC6H4 where Y= H, Me, OMe, F, Cl, Br, NO2] are cyclocondensed with hydroxylamine hydrochloride to afford the 3-aryl-5-hydroxy-5-trihalomethyl-4,5-dihydroisoxazoles 3a-g, 4a-f in good yield. The dehydratation of compounds 3a-g with concentrated sulfuric acid, led the corresponding 3-aryl-5-trichloromethylisoxazoles 5a-g . An alternative one-pot procedure yields 3-aryl-5-trihalomethylisoxazoles 5,6a-g directly by cyclocondesation of 1,2a-g with hydroxylamine hydrochloride in the presence of an excess of concentrated hydrochloric acid. 相似文献
89.
D. Freitas Siqueira D. W. Schubert V. Erb M. Stamm J. P. Amato 《Colloid and polymer science》1995,273(11):1041-1048
The techniques of neutron reflectometry and spectroscopic ellipsometry are compared as methods to measure the interface width between immiscible polymers. The interface thickness of the incompatible polymer system of polystyrene (PS) and polyn-butyl methacrylate) (PnBMA) is determined by neutron reflectrometry to (6.4±0.2) nm and (8.6±0.2) nm at temperatures of 120 and 156°C, respectively. Some emphasis is put on the measurement of those values also by spectroscopic ellipsometry using the same materials. A special sample geometry is chosen for ellipsometric measurements to compensate for thickness changes of films during annealing, and the dispersions of PS and PnBMA films are determined. With respect to the determination of the interface widths, however, it turns out that in the available wavelength range of 280 to 700 nm spectroscopic ellipsometry is not sensitive enough to measure the thin interface width between PS and PnBMA films. Neutron reflectivity results obtained for PS/PnBMA are discussed with respect to the Flory-Huggins segment interaction parameter calculated within the approximations of meanfield theory. 相似文献
90.
J. R. Locatelli E. C. Rodrigues A. B. Siqueira E. Y. Ionashiro G. Bannach M. Ionashiro 《Journal of Thermal Analysis and Calorimetry》2007,90(3):737-746
Solid-state Ln(Bz)3·H2O compounds where Ln stands for trivalent yttrium or lanthanides and Bz is benzoate have been synthesized. Simultaneous thermogravimetry-differential
thermal analysis (TG-DTA), X-ray powder diffractometry, infrared spectroscopy and chemical analysis were used to characterize
and to study the thermal behaviour of these compounds. The results led to information about the composition, dehydration,
thermal stability and thermal decomposition of the isolated compounds. 相似文献