Uma experiência com mapas conceituais na formacão inicial de professores de ciências: a argumentaçao como temática

O objetivo deste estudo é apresentar considerações sobre a potencialidade do uso do Mapa Conceitual como instrumento fornecedor de evidências da aprendizagem de licenciandos em Ciências Exatas, no que concerne à temática argumentação em aulas de Ciências. Fizeram parte deste estudo cinco licenciandos que individualmente confeccionaram um mapa sobre aspectos fundamentais para se criar um ambiente argumentativo em sala de aula. Foi possível identificar pelo mapa os conceitos representativos dos conteúdos sobre a argumentação abordados pelos licenciandos e como estes os relacionavam entre si, indicando o grau de entendimento do conteúdo de cada um. Além disso, considera-se que o mapa também contribuiu para a aprendizagem dos licenciandos uma vez que tiveram que organizar de forma interligada os diversos conceitos

Optical And Esr Study Of Er3+ In Linbo3

We report laser-excited optical transitions between the 4S3/2 and 4I15/2 multiplets of Er3+ as an impurity in the LiNbO3 host, together with the optical-absorption spectra at liquid-helium and liquid-nitrogen temperatures. The optical data allow us to determine the crystal-field splittings of those levels and the spin-Hamiltonian parameters for the 4I15/2 lower multiplet. The observed electron-spin resonance and the angular variation of this spectrum agree with the parameters obtained by optical techniques. Both techniques show that only one of the three possible trigonal sites in LiNbO3 is occupied by Er3+ within the experimental sensitivity, in agreement with recent x-ray standing-wave measurements. © 1995 The American Physical Society.5153206320

Microwave dielectric permittivity and photoluminescence of Eu 2O3 doped laser heated pedestal growth Ta 2O5 fibers

Partilhar documento na coleção da comunidade Laboratório Associado I3NWe report the microwave dielectric properties and photoluminescence of undoped and europium oxide doped Ta2O5 fibers, grown by laser heated pedestal growth technique. The effects of Eu2O3 doping 1–3 mol % on the structural, optical, and dielectric properties were investigated. At a frequency of 5 GHz, the undoped material exhibits a dielectric permittivity of 21 and for Eu2O3 doped Ta2O5 samples it increases, reaching up to 36 for the highest doping concentration. Nevertheless, the dielectric losses maintain a very low value. For this wide band gap oxide, Eu3+ optical activation was achieved and the emission is observed up to room temperature. Thus, the transparency and high permittivity make this material promising for electronic devices and microwave applications. © 2008 American Institute of Physics.FCT-PTDC/FIS/66262/06FCT-PTDC/CTM/66195/200

Structural and optical properties on thulium-doped LHPG-grown Ta2O5 fibres

Structural, spectroscopic and dielectric properties of thulium-doped laser-heated pedestal Ta2O5 as-grown fibres were studied. Undoped samples grow preferentially with a single crystalline monoclinic structure. The fibre with the lowest thulium content (0.1 at%) also shows predominantly a monoclinic phase and no intra-4f12 Tm3+ recombination was observed. For sample with the highest thulium amount (1.0 at%), the appearance of a dominant triclinic phase as well as intraionic optical activation was observed. The dependence of photoluminescence on excitation energy allows identification of different site locations of Tm3+ ions in the lattice. The absence of recombination between the first and the ground-state multiplets as well as the temperature dependence of the observed transitions was justified by an efficient energy transfer between the Tm3+ ions. Microwave dielectric properties were investigated using the small perturbation theory. At a frequency of 5 GHz, the undoped material exhibits a dielectric permittivity of 21 and for thulium-doped Ta2O5 samples it decreases to 18 for the highest doping concentration. Nevertheless, the dielectric losses maintain a very low value.FCT - PTDC/CTM/66195/2006FCT - PTDC/FIS/66262/2006FCT - PTDC/FIS/72843/200

Automatic diameter control system applied to the laser heated pedestal growth technique

We described an automatic diameter control system (ADC), for the laser heated pedestal growth technique, that reduces the diameter fluctuations in oxide fibers grown from unreacted and non-sinterized pedestals, to less than 2% of the average fiber diameter, and diminishes the average diameter fluctuation, over the entire length of the fiber, to less than 1%. The ADC apparatus is based on an artificial vision system that controls the pulling speed and the height of the molten zone within a precision of 30 mum. We also show that this system can be used for periodic in situ axial doping the fiber. Pure and Cr3+ doped LaAlO3 and pure LiNbO3 were usedas model materials

Synthesis, crystal growth and characterization of gamma-phase bismuth titanium oxide with gallium

Gallium solubility in the Bi12TiO20 (BTO) matrix was investigated by solid state reaction synthesis and Bi12Ti(1-x)Ga xO20 (BTGaO) single crystals were grown by Top Seeded Solution Growth (TSSG). We determined that it is possible to obtain a continuous solid solution from (x)Bi12TiO20: (1-x)Bi12[Ga0.7Bi0.3]O20 and that Ga replaces Ti in the BTO matrix giving Bi12Ti(1-x)Ga(x)O20 up to x < 0.2. BTGaO single crystals grown with an excess of Bi2O3 were transparent, a bleaching effect was observed due to the presence of gallium in the crystalline sillenite structure and their lattice parameter was higher than for pure BTO. The results for BTGaO single crystals showed an increase in the optical activity from rho0 = 6.4° ± 0.3°/mm, for BTO, to rho0 = 9.7° ± 0.3°/mm, for BTGaO grown with x = 0.30 in the melt. The BTGaO crystal presented an activation energy value of 0.48 ± 0.02 eV for 100 °C <= T <= 300 °C