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141.
The phase transformation from the non-polar α-phase to the polar electroactive β-phase of polyvinylidene fluoride (PVDF) has been investigated using the fluorescence from Nile red. Films of α-PVDF doped with Nile red were stretched at controlled rates at a temperature of 80 °C to produce the α- to β-phase transition. The thermo/mechanical dependent changes in the crystalline structure are related to the physical rotation of the polar (CH2-CF2) group, which can be monitored by steady state fluorescence techniques. The degree of phase transformation is related to variation in the fluorescence, which in turn is linked to local dielectric constant of the polymer. The variation of the refractive index is more associated to the alignment of the polymeric chains than to the phase transformation. Thus, fluorescence is a suitable technique to monitor phase transitions coupled to a variation in the polarity of the dielectric medium. 相似文献
142.
We present a two-Higgs-doublet model, with a Z3 symmetry, in which CP violation originates solely in a soft (dimension-2) coupling in the scalar potential, and reveals itself solely in the CKM (quark mixing) matrix. In particular, in the mass basis the Yukawa interactions of the neutral scalars are all real. The model has only eleven parameters to fit the six quark masses and the four independent CKM-matrix observables. We find regions of parameter space in which the flavour-changing neutral couplings are so suppressed that they allow the scalars to be no heavier than a few hundred GeV. 相似文献
143.
144.
We use the first-order shear deformation theory and a meshless method based on radial basis functions in a pseudospectral framework for predicting the free vibration behavior of thick orthotropic, monoclinic and hexagonal plates. The shape parameter is obtained by an optimization procedure. The three translational and two rotational degrees of freedom of a point of the laminate are independently approximated. Through numerical experiments, the capability and efficiency of the radial basis functions—pseudospectral method for eigenvalue problems are demonstrated, and the numerical accuracy and convergence are examined. 相似文献
145.
Soraa Bouattour Wannes Kallel Ana Maria Botelho do Rego L.F. Vieira Ferreira I. Ferreira Machado Sami Boufi 《应用有机金属化学》2010,24(10):692-699
This work reports on the synthesis of Li‐doped TiO2 nanoparticles using the sol–gel process and solid‐state sintering, and investigates their potential use as a photocatalyst for degradation under sunlight excitation of different organic model compounds in aqueous solution. The structure of the nanocrystals was examined by X‐ray diffraction, UV‐vis ground state diffuse reflectance absorption spectra and X‐ray photoelectron emission spectroscopy. Results showed that samples prepared by sol–gel process and calcined at 400 °C are composed of a mixture of anatase and rutile phases, in contrast to the one prepared by solid‐state sintering, which exhibits an anatase phase with Li being involved in a spinel phase. The photocatalytic degradation of aqueous solutions of different aromatic compounds was successfully achieved under sunlight excitation in presence of Li‐doped TiO2 prepared via sol–gel process. It was shown that the calcination temperature and the preparation mode greatly affect the photocatalytic efficiency. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
146.
Optical characterization of sol gel TiO<Subscript>2</Subscript> monoliths doped with Brilliant Green
S. A. Tomás O. Zelaya R. Palomino R. Lozada O. García J. M. Yáñez A. Ferreira da Silva 《The European physical journal. Special topics》2008,153(1):255-258
Amorphous titanium dioxide monoliths doped with brilliant green (BG) were synthesized by the sol-gel process. The optical
properties of the monoliths were characterized by Photoacoustic Spectroscopy and Photoluminescence Spectroscopy. The absorption
spectra for the BG-doped TiO2 monoliths exhibited two well defined absorption regions: a band below 400 nm corresponding to TiO2 absorption and three absorption bands centered at 424 nm, 588 nm, and 632 nm due to brilliant green. While the undoped TiO2 monoliths showed no luminescence, the doped samples showed a strong luminescence band at 673 nm, which increased its intensity
for increasing organic dye doping. 相似文献
147.
In conformational analysis, the systematic search method completely maps the space but suffers from the combinatorial explosion problem because the number of conformations increases exponentially with the number of free rotation angles. This study introduces a new methodology of conformational analysis that controls the combinatorial explosion. It is based on a dimensional reduction of the system through the use of principal component analysis. The results are exactly the same as those obtained for the complete search but, in this case, the number of conformations increases only quadratically with the number of free rotation angles. The method is applied to a series of three drugs: omeprazole, pantoprazole, lansoprazole-benzimidazoles that suppress gastric-acid secretion by means of H+, K+-ATPase enzyme inhibition. 相似文献
148.
Santos MG Balbi A Borrill J Ferreira PG Hanany S Jaffe AH Lee AT Magueijo J Rabii B Richards PL Smoot GF Stompor R Winant CD Wu JH 《Physical review letters》2002,88(24):241302
We use the measurement of the cosmic microwave background taken during the MAXIMA-1 flight to estimate the bispectrum of cosmological perturbations. We propose an estimator for the bispectrum that is appropriate in the flat sky approximation, apply it to the MAXIMA-1 data, and evaluate errors using bootstrap methods. We compare the estimated value with what would be expected if the sky signal were Gaussian and find that it is indeed consistent, with a chi(2) per degree of freedom of approximately unity. This measurement places constraints on models of inflation. 相似文献
149.
We study the antiferromagnetic q-state Potts model on the square lattice for q=3 and q=4, using the Wang–Swendsen–Kotecký (WSK) Monte Carlo algorithm and a powerful finite-size-scaling extrapolation method. For q=3 we obtain good control up to correlation length 5000; the data are consistent with ()=Ae
2
p
(1+a
1
e
–
+ ...) as , with p1. The staggered susceptibility behaves as
stagg
5/3. For q=4 the model is disordered (2) even at zero temperature. In appendices we prove a correlation inequality for Potts antiferromagnets on a bipartite lattice, and we prove ergodicity of the WSK algorithm at zero temperature for Potts antiferromagnets on a bipartite lattice. 相似文献
150.
N.P. Ferreira H.G.C. Human L.R.P. Butler 《Spectrochimica Acta Part B: Atomic Spectroscopy》1980,35(5):285-295
A special source in which the Grimm-type plasma is viewed side-on for spectroscopic measurements was constructed. The kinetic gas temperatures and electron densities were derived from the line profiles of Ar I 415.8 nm and He I 447.1 nm respectively. 相似文献