Simple optical apparatus for trepanning and percussion microdrilling using pulsed green Nd:YAG laser

Laser microdrilling is becoming an important tool in a wide spectrum of industrial applications due to the possibility to produce microholes in almost any type of materials. The purpose of this study was to create a simple and efficient optical apparatus that could produce microdrillings by either percussion or trepanning methods. The developed system is composed by a nanosecond Nd:YAG laser operating at 532 nm and one convergent lens with off-center optical axis of 1′. For the trepanning method the lens spins in its geometrical center at constant angular speed of 350 rpm. Typical microholes diameters obtained in metallic aluminum were in the range of 22 to 95 μm and 70 to 150 μm for the percussion and trepanning methods, respectively. Typical drilling velocities were in the order of 10 μm/s for applied fluences ranging from 22 to 150 J/cm2 for both methods. The values of the ratio between input and output diameters were 0.30 and 0.25 for microholes obtained by percussion and trepanning methods, respectively. The best microholes morphology was obtained using the trepanning method. The results for both methods are discussed based on the optical and thermal properties of the material processed and the constructed apparatusFAPESPCNP

Idade e crescimento do boca-negra, Helicolenus dactylopterus dactylopterus (Delaroche, 1809) dos Açores

A idade e o crescimento de boca-negra, Helicolenus dactylopterus dactylopterus (Delaroche, 1809), foram estudadas pela observação dos otólitos (sagittae) esquerdos inteiros (n = 401) obtidos de exemplares (14-47 cm de comprimento total) capturados em águas Açoreanas. Enumeraram-se os anéis opacos observados na face anti-sulcal dos otólitos. Os intervalos de idades foram 3-14 anos para machos e 3-12 anos para fêmeas. Estimaram-se e compararam-se os parâmetros da equação de crescimento de von Bertalanffy, entre sexos e entre métodos (leitura directa de otólitos, retrocálculo e análise de distribuições de frequências de comprimentos). Não se verificaram diferenças importantes. Os resultados são diferentes da literatura publicada para a região. Discutem-se as causas e implicações dos resultados obtidos.ABSTRACT: Bluemouth, Helicolenus dactylopterus dactylopterus (Delaroche, 1809), age and growth were studied by whole-view examination of left sagittae (n = 401) obtained from specimens (14-47 cm in total length) caught off the Azores. Opaque rings observed on the anti-sulcal surface of sagittae were enumerated as age estimates. Ages ranged from 3 to 14 years in males and 3 to 12 years in females. The von Bertalanffy growth equation was fitted to average length at age data, and compared between sexes and methods (direct examination of otoliths, backcalculation and length-frequency analysis). No important differences in growth between sexes were found. Results are different from published literature for the region. The causes and implications of the results are discussed

Effects of different tooth bleaching systems on the roughness and superficial morphology of enamel and a restorative composite resin

Objetivo: Avaliar as alterações de rugosidade e morfologia superficial do esmalte e da resina composta após diferentes técnicas de clareamento dental. Material e método: incisivos bovinos íntegros foram selecionados, sendo que cavidades padronizadas foram confeccionadas na face vestibular, as quais foram restauradas com resina composta. Os dentes foram distribuídos em grupos, de acordo com o tratamento proposto: G1-clareamento com peróxido de carbamida (PC) 10%; G2 - clareamento com peróxido de hidrogênio (PH) a 38%; G3- clareamento com PH a 38% associado à foto-ativação com LED. Para G1, o agente clareador foi aplicado por 8 horas diárias durante 21 dias. Para\ud G2 e G3, foram realizadas 3 sessões de clareamento, caracterizadas por 3 aplicações do gel clareador por 15 minutos, com intervalos de 7 dias entre as sessões, sendo que em G3 o gel clareador foi ativado com LED (470nm) por 6 minutos. As superfícies do esmalte e da resina composta foram avaliadas antes e após o procedimento clareador através de um rugosímetro e de um microscópio de força atômica. Resultados: Os resultados demonstraram diferença significante da rugosidade do esmalte antes e após o clareamento apenas para G1, em relação ao controle (Wilcoxon, p<0,05). Para a resina composta, nenhum dos grupos apresentou diferença estatística em relação ao controle (Mann-Whitney, p>0,05). Conclusão: O aumento da rugosidade do esmalte aconteceu apenas quando o clareamento foi realizado através da aplicação de um gel com 10% de PC. Nenhum dos procedimentos clareadores avaliados nesta pesquisa interferiram na rugosidade e morfologia da resina composta.CNPq (135181/2010-0; 30129/2010-1

Raman and infrared phonon features in a designed cubic polymorph of CaTa2O6

At room temperature, calcium tantalite (CaTa2O6) is known to exhibit three stable polymorphs, depending on the crystal growth conditions. In this work, the laser-heated pedestal growth method was used to obtain CaTa2O6 single crystal fibers in its quenched (ordered) cubic polymorph, attractive for optical applications. X-ray diffraction, Raman scattering and infrared spectroscopy showed that the fibers grew into the centrosymmetrical Pm3 space group. The growth axis was determined as [001]. The cylindrical fibers (20 mm long and 400 μm wide) showed good optical quality, without cracks or striations, but with small facets, parallel to crystal edges or to in-plane edge bicetrices. A comprehensive set of the optical phonons for this cubic structure was obtained, consisting of 13 (of 16 foreseen) triply degenerate polar phonons, and all the 21 predicted Raman modes. By using special scattering geometries, the Raman bands were attributed to their corresponding irreducible representations. In general, the phonons showed rather large damping constants, which do not compromise the designed optical applications in compact lasers but increase the losses in the microwave range, even though the dielectric response is quite adequate for microwave applications. Quenched defects and crystal polymorphism can be at the origin of the large phonon damping.CNPqFINEPFAPEMIGFAPES

Growth and magnetic properties of bulk electron doped 'LA IND. 0.7''CE IND. 0.3''MN''O IND. 3' manganites

We report on the growth of bulk samples (composite fibers) of the nominal composition La0.7Ce0.3MnO3 (LCMO) manganites (with Curie temperature TC,max = 300 K) by using the laser heated pedestal growth (LHPG) technique. Samples composition was verified through scanning electron microscopy with energy dispersive X-ray (EDX) analysis. The magnetic behavior of the fibers was probed by magnetization measurements. In addition to a weak ferromagnetic transition at TC0 = 45 K (due to MnO2 impurities), two more transitions with TC1 = 126 K and TC2 = 180 K were identified and linked to regions with cerium concentration of x = 0.063 and 0.13, respectively.FAPESPCAPESCNP

Surface modification and crystallization of the BaO-B2O3-SiO2 glassy system using CO2 laser irradiation

The surface modification and crystallization process of BaO-B2O3-SiO2 glass compositions when exposed to CO2 laser irradiation was evaluated as a function of the laser power, irradiation time and surface condition. The glass surface was modified by the application of laser power exceeding 0.40 W and an irradiation time of more than 300 s. Micro-Raman and X-ray diffraction measurements revealed at high laser power the formation of beta-BaB2O4 (beta-BBO) crystalline phase. The crystallization of the irradiated region was enhanced when beta-BBO micrometer sized particles were dispersed on the surface of the glass sample. The intensity of the second harmonic generation observed in the crystallized region was found to depend mainly on the condition of the glassy surface prior to glass irradiation. (C) 2007 Elsevier B.V. All rights reserved

Thick film laser sintering: an evidence for two-step process

The results for the sintering of Bi4Ti3O12 (BIT)-doped BaTi0.85Zr0.15O3 (BTZ) thick films, deposited by electrophoresis, using as heating source a CO2 laser are presented. The thermal process associated to the laser scanning sintering (LSS) acted in a similar way as a two-step-sintering process. This characteristic together with the high heating rate allowed us to obtain thick films with an average grain size of 200 nm, high relative density (~96%) and with a homogeneous microstructure. The X ray diffraction profile analysis show evidences for Bi3+ replacing Ba2+ at the A sites.FAPESPCNP

Influence of ceria addition on thermal properties and local structure of bismuth germanate glasses

Bismuth germanate glasses are interesting materials due to their physical properties and their unique structural characteristics caused by the coordination changes of bismuth and germanium atoms. Glasses of the bismuth germanate system were prepared by melting/molding method and were investigated concerning their thermal and structural properties. The structural analysis of the samples was carried out by micro-Raman and Fourier transform infrared spectroscopes. It was observed that the glass structure is formed basically by GeO(4) tetrahedral units also having the formation of the GeO(6) octahedral units. BiO(2) was considered a network former by observing the presence of octahedral BiO(6) and pyramidal BiO(3) groups in the local structure of the samples. An absorption band observed at 1103 cm(-1) in the IR spectrum of the undoped glass was attributed to the Bi-O-Ge and/or Bi-O-Bi linkage vibration. The said band shifted to lower wavenumbers after the CeO(2) addition thus reflecting changes in the glass network. Cerium oxide was an efficient oxidant agent to prevent the darkening of the glasses which was probably associated to the reduction of Bi ions. However, CeO(2) was incorporated as a local network modifier in the glass structure even at concentrations of 0.2 mol%. (C) 2010 Elsevier B.V. All rights reserved

Micro Far-Infrared Reflectivity of CaNb(2)O(6) Single Crystal Fibers Grown by the Laser-Heated Pedestal Growth Technique

CaNb(2)O(6) single crystal fibers were grown by the laser-heated pedestal growth technique, directly from the starting reagents. Optically transparent fibers were obtained in the form of rods with elliptical cross-section, free from cracks, impurities, and secondary phases, with an average diameter of 0.4 mm and about 20 mm of length. The fibers grew within the orthorhombic Pbcn columbite structure, with the growth axis nearly parallel to the crystallographic a-direction. The parameters b and c were parallel to the shorter and larger ellipsis axes. A special setup using a microscope was developed to obtain the far-infrared reflectivity spectra of these micrometer-sized fibers, allowing the identification and assignment of 34 of the 38 polar phonons foreseen for the material. From these phonons, the intrinsic dielectric constant (<epsilon(r)> = 18.2) and quality factor (<Q(u) x f> of 185 THz) could be estimated, showing the potential of the material for applications in microwave circuitry. These results, along with previous polarized Raman data (Cryst. Growth Des. 2010, 10, 1569), allow us to present a comprehensive set of optical phonon modes and to discuss the potential use of designed CaNb(2)O(6) microcrystals in compact optical devices.Brazilian agency CNPqConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Financiadora de Estudos e Projetos (FINEP)Brazilian agency FINEPBrazilian agency FAPESPFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Brazilian agency FAPEMIGFundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG