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671.
H.‐D. Pfannes J.H. Dias Filho J.L. López S.L. Pereira P.C. Morais F.A. Tourinho 《Hyperfine Interactions》1998,113(1-4):507-515
The parameters of the log‐normal size distribution of a MnFe2O4 ferrofluid powder sample have been determined by X‐ray diffraction. The mean blocking temperature was determined from the maximum of Xi . Mössbauer spectra at 4.2–300 K are interpreted by a new simple theory of superparamagnetism and taking a reduction of the internal magnetic field for small particles, a size dependence of the anisotropy constant, the size distribution and collective excitations into account. 相似文献
672.
J. B. Bastos Filho A. Rodriguez W. Baltensperger 《Zeitschrift für Physik B Condensed Matter》1980,39(3):207-211
The high frequency response of an electron gas with elastic scatterers can be described by a Drude equation with a memory term, which is an integral over a kernel times the square of the scattering potential. In the momentum (and frequency or time) representation, this kernel is discontinuous at the diameter of the Fermi sphere.In the time representation it has the causality property. As a function of space it shows Friedel oscillations. 相似文献
673.
M. Álvarez F. M. de Carvalho Filho L. Griguolo 《Communications in Mathematical Physics》1996,178(2):467-481
The propagation of a localized wave packet in the conical space-time created by a pointlike massive source in 2+1 dimensional gravity is analyzed. The scattering amplitude is determined and shown to be finite along the classical scattering directions due to interference between the scattered and the transmitted wave functions. The analogy with diffraction theory is emphasized.This work is supported in part by funds provided by the U. S. Department of Energy (D.O.E.) under cooperative agreement #DE-FC02-94ER40818. 相似文献
674.
F. M. Carvalho Filho 《Zeitschrift fur Physik C Particles and Fields》1997,74(1):185-190
Based on the covariant background field method, we calculate the ultraviolet counterterms up to two-loop order and discuss the renormalizability of the three-dimensional non-linear sigma models with arbitrary Riemannian manifolds as target spaces. We investigate the bosonic model and its supersymmetric extension. We show that at the one-loop level these models are renormalizable and even finite when the manifolds are Ricci-flat. However, at the two-loop order, we find non-renormalizable counterterms in all cases considered, so the renormalizability and finiteness of such models are completely lost in this order. 相似文献
675.
M. Behar J. P. Biersack P. F. P. Fichtner D. Fink C. V. De B. Leite Filho C. A. Olivieri 《辐射效应与固体损伤》2013,168(3):117-122
Depth distribution profiles of 15 to 350 keV 69Ga+ implanted at room temperature in amorphized silicon have been measured by 4He ion Rutherford backscattering. The measured projected ranges and range stragglings are in excellent agreement with the predictions calculated via realistic Monte Carlo simulations, TRIM code. 相似文献
676.
Natasha Coral Elizabeth Rodrigues Victor Rumjanek José Roberto Zamian Geraldo Narciso da Rocha Filho Carlos Emmerson Ferreira da Costa 《Magnetic resonance in chemistry : MRC》2013,51(2):69-71
Production of alternative fuels, such as biodiesel, from transesterification of vegetable oil driven by heterogeneous catalysts is a promising alternative to fossil diesel. However, achieving a successful substitution for a new renewable fuel depends on several quality parameters. 1H NMR spectroscopy was used to determine the amount of methyl esters, free glycerin and acid number in the transesterification of soybean oil with methanol in the presence of hydrotalcite‐type catalyst to produce biodiesel. Reaction parameters, such as temperature and time, were used to evaluate soybean oil methyl esters rate conversion. Temperatures of 100 to 180 °C and times of 20 to 240 min were tested on a 1 : 12 molar ratio soybean oil/methanol reaction. At 180 °C/240 min conditions, a rate of 94.5 wt% of methyl esters was obtained, where free glycerin and free fatty acids were not detected. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
677.
Gomes Constantino M da Silva Filho LC Neto AC Gomes Heleno VC da Silva GV Callegari Lopes JL 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(1-2):171-176
A detailed NMR analysis with total assignment of (1)H and (13)C NMR data for the endo and the exo adducts, obtained by Diels-Alder reaction between 2-cyclohexenone and cyclopentadiene, is described. The unequivocal assignment of the endo and exo structures was performed by (1)H and (13)C NMR. These assignments were supported by theoretical chemical shift calculations at GIAO/HF level using 6-311 + g(2d, p) from optimized structures at the B3LYP/6-31g(d) level. 相似文献
678.
A. E. S. Vives S. Moreira S. M. B. Brienza O. L. A. D. Zucchi V. F. Nascimento Filho 《Journal of Radioanalytical and Nuclear Chemistry》2006,270(1):231-236
Summary This study uses fishes as indicators of metal contamination in the Piracicaba Basin and also for evaluation of the risks to
human health by the ingestion of fish contaminated by metals and other potentially toxic elements. Based on total reflection
X-ray fluorescence analysis, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn and Ba were detected and evaluated in
the muscle and viscus (liver, intestine and stomach) of fish collected in the Piracicaba River. 相似文献
679.
Vicente C Sebastián B Fontaniella B Márquez A Xavier Filho L Legaz ME 《Journal of chromatography. A》2001,917(1-2):55-61
Bioskin is a natural product produced by a mixed culture of Acetobacter xylinum, Saccharomyces cerevisiae and S. pombe cultured on media containing sucrose. It is of fibrillar nature able to retain some proteins, such as cytochrome c, by adsorption, and mainly composed of glucosamine and N-acetyl-D-glucosamine. This makes it possible that, at an adequate pH value, proteins charged as polyanionic molecules, such as catalase, can be retained by ionic adsorption using the positively charged amino groups of the matrix. In addition, bioskin can also be used as an affinity matrix to retain glycoproteins able to perform specific affinity reactions with the amino sugars of the matrix, such as invertase, fetuin or ovalbumin. Its possible use as a chromatographic support is discussed. 相似文献
680.
Tiago A.S. Brandão Angela Malheiros Jacir Dal Magro Valdir Cechinel Filho Rosendo A. Yunes 《Journal of inclusion phenomena and macrocyclic chemistry》2003,46(1-2):77-81
Polygodial is a sesquiterpene drimane isolated from the genus Drimys, whichexhibits anti-asthmatic, anti-allergic, anti-inflammatory and antinociceptive effects.We have prepared a polygodial--cyclodextrin inclusion complex for furtherpharmacological studies. The inclusion complex was synthesized by co-precipitationand analyzed by Thermogravimetric Analysis, showing a decrease in the number ofwater molecules of hydration in relation to the native -cyclodextrin. DifferentialThermogravimetric Analysis indicated a peak corresponding to the evaporation ofpolygodial. With Differential Scanning Calorimetry, the melting peak to polygodial was not observed, however, there was an increase in the energy of vaporization of the water molecules in relation to native -cyclodextrin. Using a Scanning Electron Microscopy a clear difference in the morphology of crystals of the inclusion complex and native -cyclodextrin could be seen. The association constant between polygodial and -cyclodextrin, measured by UV spectroscopy was 1,006 M-1 at 37 °C, pH 7.0 and ionic strength 0.2 M, following stoichiometry 1:1. 相似文献