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171.
Cecí lia Ferreira Armando Machado 《Proceedings of the American Mathematical Society》2000,128(7):2181-2186
Let denote the set of all -roots of the identity in a Lie group . We show that is always an embedded submanifold of , having the conjugacy classes of its elements as open submanifolds. These conjugacy classes are examples of -symmetric spaces and we show, more generally, that every -symmetric space of a Lie group is a covering manifold of an embedded submanifold of . We compute also the Hessian of the inclusions of and into , relative to the natural connection on the domain and to the symmetric connection on .
172.
R. Menegotto Costa L. Mendon?a Ferreira V. N. Vieira P. Pureur J. Schaf 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(2):107-113
We have studied experimentally the electrical magneto-conductivity near the
superconducting transition of YBa2Cu3O7-δ, YBa2
(Cu2.95Zn0.05)O7-δ and Y(Ba1.75Sr0.25)Cu3O7-δ polycrystalline samples. The measurements were performed in magnetic fields ranging from 0 to 400 Oe applied parallel to
the current orientation. The results show that the resistive transition of these systems proceeds in two stages. The pairing
transition occurs at the bulk critical temperature Tc, where superconductivity is stabilized within small and homogeneous regions of the
sample generically called grains. The regime of approach to the zero resistance state reveals the occurrence of a coherence
transition at a lower temperature Tc0. This transition is related to the connective nature of the granular samples and is controlled by fluctuations of the
order-parameter phase of individual grains. Our experiments show that the Zn-doping, besides depressing the pairing critical
temperature, strongly enlarges the temperature range dominated by effects related to the coherence transition. The substitution
of Ba by Sr causes only a small reduction of Tc, but also enhances significantly the effects related to the grain
coupling phenomenology. In general, our results indicate that these impurity substitutions in YBa2Cu3O7-δ produce or magnify the granularity at a microscopic level, enhancing the effects of phase fluctuations in the conductivity
near the transition. 相似文献
173.
This paper introduces a relative structural complexity measure for the characterization of disordered surfaces. Numerical solutions of 2d+1 KPZ equation and scanning force microscopy (SFM) patterns of porous silicon samples are analyzed using this methodology. The results and phenomenological interpretation indicate that the proposed measure is efficient for quantitatively characterize the structural complexity of disordered surfaces (and interfaces) observed and/or simulated in nano, micro and ordinary scales. 相似文献
174.
Lorena M. A. Silva Elenilson G. A. Filho Sérgio S. Thomasi Bianca F. Silva Antonio G. Ferreira Tiago Venâncio 《Magnetic resonance in chemistry : MRC》2013,51(9):541-548
The informal (and/or illegal) e‐commerce of pharmaceutical formulations causes problems that governmental health agencies find hard to control, one of which concerns formulas sold as natural products. The purpose of this work was to explore the advantages and limitations of DOSY and HPLC–UV–SPE–NMR. These techniques were used to identify the components of a formula illegally marketed in Brazil as an herbal medicine possessing anti‐inflammatory and analgesic properties. DOSY was able to detect the major components present at higher concentrations. Complete characterization was achieved using HPLC–UV–SPE–NMR, and 1D and 2D NMR analyses enabled the identification of known synthetic drugs. These were ranitidine and a mixture of orphenadrine citrate, piroxicam, and dexamethasone, which are co‐formulated in a remedy called Rheumazim that is used to relieve severe pain, but it is prohibited in Brazil because of a lack of sufficient pharmacokinetic and pharmacodynamic information. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
175.
Joana Lia Ferreira Maria João Melo Ana Maria Ramos 《Polymer Degradation and Stability》2010,95(4):453-461
The photochemistry of poly(vinyl acetate), PVAc, homopolymer, of PVAc mixtures with selected pigments and fillers, and of accurate historic reproductions based on the colours prepared by Portuguese artist Joaquim Rodrigo and on those supplied by the company A Favrel was studied. The systems, applied as films, were irradiated at λ ≥ 300 nm and the changes followed by size exclusion chromatography, infrared spectroscopy, and colorimetry.PVAc as homopolymer or as an emulsion paint proved to be very stable to light, and after 5000 h of irradiation no gel fraction was observed. ΦR (λirr = 313 nm) for chain scission for PVAc was determined to be 7 × 10−8. This value indicates that the mechanism/s operating when irradiating at λ ≥ 300 nm are different from those previously published with irradiation involving 254 nm. No side-group scission was observed, and main chain scission is the foremost photodegradation mechanism. Also, the metal ions present in the pigments do not affect the photochemical stability of the polymer. 相似文献
176.
Jeanine Giarolla Daniela G. Rando Kerly F.M. Pasqualoto Márcio H. Zaim Elizabeth I. Ferreira 《Journal of Molecular Structure》2010,939(1-3):133-138
Molecular modeling methodologies were applied to perform preliminary studies concerning the release of active agents from potentially antichagasic and antileishmanial dendrimer prodrugs. The dendrimer was designed having myo-inositol as a core, l-malic acid as a spacer group, and hydroxymethylnitrofurazone (NFOH), 3-hydroxyflavone or quercetin, as active compounds. Each dendrimer presented a particular behavior concerning to the following investigated properties: spatial hindrance, map of electrostatic potential (MEP), and the lowest unoccupied molecular orbital energy (ELUMO). Additionally, the findings suggested that the carbonyl group next to the active agent seems to be the most promising ester breaking point. 相似文献
177.
V. Pedroni P. C. Schulz M. E. Gschaider de Ferreira M. A. Morini 《Colloid and polymer science》2000,278(10):964-971
We synthesised a porous siliceous material via hydrothermal hydrolysis of sodium silicate, using chitosan as a template.
As far as we know, this is the first synthesis of siliceous porous material using chitosan as a template in a hydrothermal
way. A fibrous material was obtained, whose macroscopic fibres were formed by a spongelike siliceous network with pores having
a radius of 0.57 μm. The siliceous walls of the pores were, in turn, of the form of a microporous–mesoporous material; the
pore radius distribution was polymodal with maxima at 0.84, 1.0, 1.2 and 1.5 nm and a broad band between 3 and 10 nm. This
structure may be due to the aggregation of the hydrated chitosan helices in bundles of parallel fibres with different size
and the gelation of the system. The aggregation process might be induced by the addition of silicate.
Received: 12 January 2000/Accepted: 7 March 2000 相似文献
178.
Leonardo C. Ferreira Carlos A. L. Filgueiras Lorenzo C. Visentin Jairo Bordinho Manfredo Hrner 《无机化学与普通化学杂志》2008,634(11):1896-1900
The preparation and characterization of two novel HgCl2 and Hg(SCN)2 complexes with bis[N‐(2‐tert‐butylphenyl)imine]acenaphthene is here described. One‐pot reaction techniques were used, leading to high yields of 75 % and 81 %, respectively. The complexes were characterized by microanalysis, i.r. and 1HNMR spectroscopy, and by single crystal X‐ray diffraction. The structures of the complexes present similar characteristics, the most outstanding being the formation of dimers via intermolecular interaction. Whereas the HgCl2 complex shows a unidimensional network due to strong π–π interactions, its Hg(SCN)2 counterpart displays a supramolecular arrangement resulting from non classical hydrogen bond formation. 相似文献
179.
Resonating valence bond theory combined with DFT calculations permit to build a simple model for the dissociation of H2 on palladium surface. Based on analysis of the electron transfer and total energy for different geometries of the Pd2–H2 and Pd5–H2 systems it is found that the predissociative state corresponds to a tilted molecule adsorbed on the surface. 相似文献
180.
Laurent Aubry Thierry Sayd Claude Ferreira Christophe Chambon Annie Vnien Sylvie Blinet Marie Bourin Anglique Travel Maeva Halgrain Vronique Sant-Lhoutellier Laetitia Thron 《Molecules (Basel, Switzerland)》2021,26(12)
The marketing of poultry livers is only authorized as fresh, frozen, or deep-frozen. The higher consumer demand for these products for a short period of time may lead to the marketing of frozen–thawed poultry livers: this constitutes fraud. The aim of this study was to design a method for distinguishing frozen–thawed livers from fresh livers. For this, the spectral fingerprint of liver proteins was acquired using Matrix-Assisted Laser Dissociation Ionization-Time-Of-Flight mass spectrometry. The spectra were analyzed using the chemometrics approach. First, principal component analysis studied the expected variability of commercial conditions before and after freezing–thawing. Then, the discriminant power of spectral fingerprint of liver proteins was assessed using supervised model generation. The combined approach of mass spectrometry and chemometrics successfully described the evolution of protein profile during storage time, before and after freezing-thawing, and successfully discriminated the fresh and frozen–thawed livers. These results are promising in terms of fraud detection, providing an opportunity for implementation of a reference method for agencies to fight fraud. 相似文献