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131.
A. L. F. Briso M. S. M. Fonseca L. C. A. G. de Almeida S. J. Mauro P. H. dos Santos 《Laser Physics》2010,20(12):2066-2069
This study evaluated the color alteration of teeth subjected to the action of different bleaching agents and the influence
of light sources commonly used in association with these products, In GI, the specimens remained immersed in artificial saliva.
The specimens in GII were bleached with a 10% carbamide peroxide gel 4 hours/day during 3 weeks; the teeth in the other three
groups were subjected to three sessions of three 10-min applications of 35% hydrogen peroxide gel at 7-day intervals. In GIII,
no light was used, while in GIV and GV the gel was associated with a quartz-tungsten-halogen light and a LED/laser source,
respectively. The teeth color was evaluated before and 7 days after the bleaching sessions by reflectance spectrophotometry.
Data were analyzed statistically by ANOVA and Fisher’s test (α = 0.05), and showed that a significant color change was obtained
in all treated groups. After the first week of treatment and at the end of it, the bleaching protocols showed similar results.
The results of the present study indicate that association of a light source is not necessary to obtain the bleaching effect
and that optimal bleaching can be achieved with all techniques tested. 相似文献
132.
Amanda L. dos Santos G. O. Chierice A. T. Riga K. Alexander Ellen Matthews 《Journal of Thermal Analysis and Calorimetry》2009,97(1):329-332
Eugenol is an allyl chain-substituted guaiacol in the biosynthesized phenylpropanoid compound class derived from Syzygium aromaticum L. and widely used in folk medicine. Nonetheless, its pharmacological use is limited by some problems, such as instability
when exposed to light and high temperature. In order to enhance stability, the eugenol molecule was structurally modified,
resulting in eugenyl acetate. The eugenyl acetate’s thermal behavior and crystal structure was then characterized by differential
scanning calorimetry (DSC) and X-ray diffraction (XRD) and compared to a commercial sample. 相似文献
133.
Irinéia R. do Nascimento Raildo M. de Jesus Walter N.L. dos Santos Anderson Santos Souza Pedro Sanches dos Reis 《Microchemical Journal》2010,96(1):37-41
In this work, the mineral composition of fresh bovine milk obtained from the milk-producing areas of the Brazilian State of Sergipe was examined. A dry-ashed digestion method and the ICP OES technique were used for the quantification of mineral elements (e.g., Ca, Mg, K, Na, P, Sr and Zn) in 27 samples of milk collected from properties located in milk-producing areas around Nossa Senhora da Glória. The following ranges of values (% m/v) were obtained: 0.063 to 0.117 for Ca; 0.060 to 0.114 for P; 0.024 to 0.064 for Na; and 0.087 to 0.164 for K. The ranges of values (mg L− 1) for the other mineral elements were also found: 0.68 to 1.89 for Sr; 2.46 to 5.73 for Zn; and 54.2 to 109.9 for Mg. Additionally, the exploratory evaluation of the 27 milk samples was performed using principal component analysis (PCA) involving seven variables dealing with the effect of different management systems (conventional and organic) on milk composition. The results show that there are indeed differences between the mineral composition of milk from properties that use organic practices and those that use conventional management practices. 相似文献
134.
135.
A new approach for studying photorefractive gratings in two-wave mixing experiments by a phase modulation technique is presented. The introduction of a large-amplitude, high-frequency sinusoidal phase modulation in one of the input beams blurs the interference pattern and provides powerful harmonic signals for accurate measurements of the grating diffraction efficiency η and the output phase shift ϕ between the transmitted and diffracted waves. The blurring of the light fringes can be used to suppress the higher spatial harmonics of the grating, allowing a space-charge field with sinusoidal profile to be recorded. Although the presence of such a strong phase modulation affects the beam coupling in a rather complicated way, it is shown that for the special case of equal intensity input beams, the effect of the phase modulation on η and ϕ is reduced to a weakening of the coupling strength. The potentialities of the technique are illustrated in a study of refractive-index waves excited by running interference patterns in a Bi12TiO20 crystal. Expressions for the diffraction efficiency and the output phase shift are derived and used to match numerically calculated curves to the experimental data. The theoretical model is supported by the very good data fitting and allows the computation of important material parameters. PACS 42.40.Ht; 42.40.Kw; 42.70.Nq 相似文献
136.
The first author was supported in part by CNPq 相似文献
137.
C.R. Mendonça U.M. Neves L. De Boni A.A. Andrade D.S. dos Santos Jr. F.J. Pavinatto S.C. Zilio L. Misoguti O.N. Oliveira Jr. 《Optics Communications》2007,273(2):435-440
In this paper we present optical anisotropy induced by 150-fs laser pulses operating at 775 nm in poly(methyl methacrylate) (PMMA) films doped with Disperse Red 13 (DR13). Two-photon absorption of DR13 induces reversible birefringence in the sample, a feature associated with the molecular orientation caused by isomerization of the azochromophores. No irreversible anisotropy, associated with photobleaching of the chromophore was observed. The slope of 2 obtained for the induced birefringence as a function of the excitation irradiance corroborates the two-photon nature of the process. 相似文献
138.
S.A. Loureiro A.Z. Salustiano D.S. dos Santos 《Journal of Physics and Chemistry of Solids》2007,68(10):1845-1855
The present work aims to correlate, in time, macroscale and microscale phenomenological evolutions of the microstructure of Fe and FeZn alloys processed by mechanical milling (MM) and alloying (MA), respectively. Powders were characterized for particle size distribution (PSD), particle morphology (optical microscopy, OM, scanning electron microscopy, SEM), microhardness, crystallite size, differential scanning calometry (DSC) and transmission electron microscopy (TEM). Two macroscopic regimes of PSD behavior were distinguished: the first one dominated by the cold welding process; and, the other where both fracture and agglomeration play a significant role. Solid solubilization of Zn on bcc Fe was found to reduce the final microhardness as well as increase the lattice parameter and is very well predicted by Miedema's thermodynamical approach. Microhardness and solid solution formation kinetics were correlated in time and both could be precisely described by a logistic function. After 5 h of planetary milling, microhardness and the lattice parameter become stable as well as the PSD and particle morphology, indicating that the system has already reached steady state. Indeed, this condition can be monitored by both macroscopic and microscopic parameters. Prior to an homogeneous powder, DSC results suggest an endothermic solid-state amorphization reaction for samples processed for up to 1 h as a result of the formation of clean Fe/Zn interfaces during MA. 相似文献
139.
Castro EV Novoselov KS Morozov SV Peres NM dos Santos JM Nilsson J Guinea F Geim AK Neto AH 《Physical review letters》2007,99(21):216802
We demonstrate that the electronic gap of a graphene bilayer can be controlled externally by applying a gate bias. From the magnetotransport data (Shubnikov-de Haas measurements of the cyclotron mass), and using a tight-binding model, we extract the value of the gap as a function of the electronic density. We show that the gap can be changed from zero to midinfrared energies by using fields of less, approximately < 1 V/nm, below the electric breakdown of SiO2. The opening of a gap is clearly seen in the quantum Hall regime. 相似文献
140.
Vicenţiu D. Rădulescu Gelson C. G. dos Santos Leandro S. Tavares 《Mathematische Nachrichten》2023,296(6):2555-2574
This paper is concerned with the existence and multiplicity of solutions for a class of problems involving the Φ-Laplacian operator with general assumptions on the nonlinearities, which include both semipositone cases and critical concave convex problems. The research is based on the subsupersolution technique combined with a truncation argument and an application of the Mountain Pass Theorem. The results in this paper improve and complement some recent contributions to this field. 相似文献