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61.
P.S. Pizani M.R. Joya F.M. Pontes L.P.S. Santos M. Godinho E.R. Leite E. Longo 《Journal of Non》2008,354(2-9):476-479
Intense photoluminescence in the visible region was observed at room temperature in standard soda-lime-silica glass powder, mechanically milled in a high-energy attrition mill. The emission band maximum shows an interesting dependence on the exciting wavelength, suggesting the possibility to tune the PL emission. These findings indicate that the photoluminescence may be directly related to unsatisfied chemical bonds correlated with the high surface area. The Raman scattering and ultraviolet–visible optical reflectance measurements corroborate this assertion. Transmission electron microscopy measurements indicate that samples milled more than 10 h present the formation of nanocrystallites with about 10–20 nm. 相似文献
62.
Igor Leite Freire 《Journal of Mathematical Analysis and Applications》2010,367(2):716-9473
Using the scalar curvature of the product manifold S2×R and the complete group classification of nonlinear Poisson equation on (pseudo) Riemannian manifolds, we extend the previous results on symmetry analysis of homogeneous wave equation obtained by H. Azad and M.T. Mustafa [H. Azad, M.T. Mustafa, Symmetry analysis of wave equation on sphere, J. Math. Anal. Appl. 333 (2007) 1180-1188] to nonlinear Klein-Gordon equations on the two-dimensional sphere. 相似文献
63.
João R. Cardoso F. Silva Leite 《Journal of Computational and Applied Mathematics》2010,233(11):2867-2875
Two widely used methods for computing matrix exponentials and matrix logarithms are, respectively, the scaling and squaring and the inverse scaling and squaring. Both methods become effective when combined with Padé approximation. This paper deals with the computation of exponentials of skew-symmetric matrices and logarithms of orthogonal matrices. Our main goal is to improve these two methods by exploiting the special structure of skew-symmetric and orthogonal matrices. Geometric features of the matrix exponential and logarithm and extensions to the special Euclidean group of rigid motions are also addressed. 相似文献
64.
Maria Hermínia de Paula Leite Mello Mário Olivero Marques da Silva 《manuscripta mathematica》2000,101(2):191-198
In this paper we consider the question of the existence of a nonstable vector bundle monomorphism u:α→β over a closed, connected and smooth manifold M, when dimension of α= 3, dimension of β= dimension of M=n≡ 0(4). The singularity method provides the full obstruction to this problem and under some homological hypothesis we can compute it in terms of well known invariants. Received: 31 May 1999 相似文献
65.
do Nascimento Marreiro Teixeira Ana Siqueira Siqueira Teixeira Paulo Ronaldo Sousa de Oliveira Farias Emanuel Airton Ferraz e Sousa Brandon Moura Sérvulo Kátia Bonfim de Leite da Silva Durcilene Alves Eiras Carla 《Journal of Solid State Electrochemistry》2020,24(5):1143-1155
Journal of Solid State Electrochemistry - The present work proposes a new electrochemical sulfite biosensor based on babassu mesocarp nanoparticles (BMNPs) immobilized on the surface of a pyrolytic... 相似文献
66.
Rodrigo O.M.A. de Souza Lilian M.C. Matos Ingrid C.R. Costa Selma G.F. Leite O.A.C. Antunes 《Tetrahedron letters》2009,50(17):2017-1605
The present Letter details our findings on the lipase-catalyzed Michael reactions between primary or secondary amines and acrylonitrile. Several lipases were evaluated, and good results were obtained leading to the formation of Michael adducts in shorter reaction times than the uncatalyzed reactions. 相似文献
67.
Rafael Libanori Tania R. Giraldi Elson Longo Edson R. Leite Caue Ribeiro 《Journal of Sol-Gel Science and Technology》2009,49(1):95-100
Commercial TiO2 nanoparticles were superficially modified through polymeric resins obtained from polymerization of citrate complexes of Y3+ and Al3+ with ethylenglycol. The materials were treated at 450 °C for 4 h to obtain modified nanoparticles, which were characterized
by HR-TEM, Zeta potential and surface area through N2 fisisorption. Rhodamine B photodegradation by visible light irradiation and in presence of those modified nanoparticles was
compared with the same process in presence of unmodified commercial TiO2 nanoparticles. It was observed, by UV–visible spectroscopy, that the catalytic photoactivity in presence of modified nanoparticles
was smaller than that observed with commercial TiO2 nanoparticles. However, the surface modifier played an important role in the photodegradation kinetic process, showing a
non-linear relation between modifier amount and photodegradation rate, presenting a maximum value at 0.8% (w/w). 相似文献
68.
Rangel M Leite A João Amorim M Garribba E Micera G Lodyga-Chruscinska E 《Inorganic chemistry》2006,45(20):8086-8097
Aqueous solution studies regarding the identification and characterization of complexes formed by the VIVO ion and 11 3-hydroxy-4-pyridinone derivatives have been performed using EPR and UV/vis spectroscopic techniques. For the three ligands (HL) adequately soluble in water (1-methyl-3-hydroxy-4-pyridinone, 1-methyl-2-ethyl-3-hydroxy-4-pyridinone, and 1,2-diethyl-3-hydroxy-4-pyridinone), potentiometric titrations were performed; the results are consistent with the formation of [V(IV)OL]+, [V(IV)OL2], [V(IV)OL2H(-1)]-, [(V(IV)O)2L2H(-2)], and [V(IV)L3]+ species. Bis chelated complexes are characterized by a cis-trans isomerism, the trans isomer being strongly favored with respect to the cis arrangement. Tris chelated non-oxo V(IV) species were prepared in CH3COOH; their spectroscopic features point to a d(z2) ground state and a geometry intermediate between an octahedron and a trigonal prism, related to the steric requirements of the substituent on the carbon atom in position 2 of the pyridinone ring. Four new solid derivatives, [V(IV)O(1,2-diethyl-3-hydroxy-4-pyridinonato)2], [V(IV)O(1-(p-tolyl)-2-ethyl-3-hydroxy-4-pyridinonato)2], [V(IV)O(1-(p-(n-butyl)phenyl)-2-ethyl-3-hydroxy-4-pyridinonato)2], and [V(IV)O(1-(p-(n-hexyl)phenyl)-2-ethyl-3-hydroxy-4-pyridinonato)2], were isolated and characterized; they exhibited a five-coordinate geometry close to square-pyramid. A criterion for establishing the degree of distortion toward the trigonal-bipyramid on the basis of the electronic absorption spectra is provided. Relationships between the pKa of the -OH group in position 3 of the ring and (i) log K of mono and bis chelated complexes, (ii) pK of the water molecule in cis-[V(IV)OL2(H2O)], (iii) log K of tris chelated species [V(IV)L3]+, and (iv) 51V hyperfine coupling constant (Az) have been established and discussed for a number of pyrone, pyridinone, and catechol ligands. The results are rationalized by assuming for pyridinones an electronic structure intermediate between that of pyrones and catechols. The relationships are valuable to the understanding of the behavior of VIVO species in aqueous solution. 相似文献
69.
70.
Costa CA Leite CA Galembeck F 《Langmuir : the ACS journal of surfaces and colloids》2006,22(17):7159-7166
The sorption of surfactants and NaCl in silica nanosized particles creates unexpected spatial distributions of solutes that were evidenced by electron spectroscopy imaging in the transmission electron microscope (ESI/TEM). The spectral images show that simple ions (Na(+), Cl(-), Br(-)) are actually absorbed within the particles irrespective of their charges, while surfactant chains are adsorbed at the particle surfaces. The expected effect of the surfactants on particle aggregation is also observed in the micrographs. In the case of salt, close-packed silica particle arrays are formed at low ionic strength, but only coarse aggregates form at higher salt concentrations. The particles absorb both Na(+) and Cl(-) ions in similar amounts, from 0.5 mol L(-)(1) NaCl, but Na(+) ions are depleted from the particles' immediate outer vicinity, where Cl(-) ions are in turn accumulated. These results confirm that St?ber silica nanoparticles are highly porous and reveal their potential usefulness as carriers of small molecules and ions, due to the small particle size, exceptional colloidal stability, and this newly found sorption behavior. 相似文献