Intergranular properties of uniaxially pressed YBa(2)Cu(3)O(7-delta) ceramic samples

We performed measurements of electrical resistivity as a function of temperature, rho(T), in polycrystalline samples of YBa(2)Cu(3)O(7-delta) (Y-123) subjected to different uniaxial compacting pressures. We observed by using X-ray diffractometry that samples have a very similar composition. Most of the identified peaks are related to the superconducting Y-123 phase. Also, from the X-ray diffraction patterns performed, in powder and pellet samples, we estimated the Lotgering factor along the (00l) direction, F((00l)). The results indicate that F((00l)) increases from 0.13 to 0.16. From electrical resistivity measurements as a function of temperature, we were able to separate contributions arising from both the grain misalignment and microstructural defects. We found appreciable degradation in the normal-state transport properties of samples with an increase in uniaxial compacting pressure. It seems that this type of behavior is associated with an increase in the influence of microstructural defects at the intergranular level. The experimental results are analyzed in the framework of a current conduction model of granular samples.

Magnetic structures of quaternary intermetallic borocarbides RCo(2)B(2)C (R = Dy, Ho, Er)

The magnetic structures of the title compounds have been studied by neutron diffraction. In contrast to the isomorphous RNi(2)B(2)C compounds, wherein a variety of exotic incommensurate modulated structures has been observed, the magnetic structure of ErCo(2)B(2)C is found to be a collinear antiferromagnet with k = (12, 0, 12) while those of HoCo(2)B(2)C and DyCo(2)B(2)C are observed to be simple ferromagnets. For all studied compounds, the moments are found to be confined within the basal plane and their magnitudes are comparable to the values obtained from the low-temperature isothermal magnetization measurements. The absence of modulated magnetic structures in the RCo(2)B(2)C series (for ErCo(2)B(2)C, verified down to 50 mK) is attributed to the quenching of the Fermi surface nesting features.

Infrared emission and defect centres in Er and Yb codoped Y(3)Al(5)O(12) phosphors

YAG phosphor powders doped/codoped with Er(3+)/(Er(3+) + Yb(3+)) have been synthesised by using the solution combustion method. The effect of direct pumping into the (4)I(11/2) level under 980 nm excitation of doped/codoped Er(3+)/Yb(3+)-Er(3+) in Y(3)Al(5)O(12) (YAG) phosphor responsible for an infrared (IR) emission peaking at similar to 1.53 mu m corresponding to the (4)I(13/2)->(4)I(15/2) transition has been studied. YAG exhibits three thermally-stimulated luminescence (TSL) peaks at around 140A degrees C, 210A degrees C and 445A degrees C. Electron spin resonance (ESR) studies were carried out to identify the centres responsible for the TSL peaks. The room temperature ESR spectrum of irradiated phosphor appears to be a superposition of two distinct centres. One of the centres (centre I) with principal g-value 2.0176 is identified as O(-) ion, while centre II with an isotropic g-factor 2.0020 is assigned to an F(+) centre (singly ionised oxygen vacancy). An additional defect centre is observed during thermal-annealing experiments and this centre (assigned to F(+) centre) seems to originate from an F-centre (oxygen vacancy with two electrons) and these two centres appear to correlate with the observed high-temperature TSL peak in YAG phosphor.

Influence of Er:YAG laser on surface treatment of aged composite resin to repair restoration

The purpose of this study was to investigate the effect of Er:YAG laser on surface treatment to the bond strength of repaired composite resin after aged. Sixty specimens (n = 10) were made with composite resin (Z250, 3M) and thermocycled with 500 cycles, oscillating between 5 to 55A degrees C. The specimens were randomly separated in six groups which suffered the following superficial treatments: no treatment (GI, control), wearing with diamond bur (GII), sandblasted with aluminum oxide with 27.5 A mu m particles (GIII) for 10 s, 200 mJ Er:YAG laser (GIV), 300 mJ Er:YAG laser (GV), and 400 mJ Er:YAG laser (GVI), with the last 3 groups under a 10 Hz frequency for 10 s. Restoration repair was done using the same composite. The shear test was done into the Universal testing machine MTS-810. Analyzing the results through ANOVA and Tukey test, no significant differences were found (p-value is 0.5120). Average values analysis showed that superficial treatment with aluminum oxide presented the highest resistance to shear repair interface (8.91MPa) while 400 mJ Er:YAG laser presented the lowest (6.76 MPa). Fracture types analysis revealed that 90% suffered cohesive fractures to GIII. The Er:YAG laser used as superficial treatment of the aged composite resin before the repair showed similar results when used diamond bur and sandblasting with aluminum oxide particles.

Optical and dielectric relaxor behaviour of Ba(Zr(0.25)Ti(0.75))O(3) ceramic explained by means of distorted clusters

In this work, Ba(Zr(0.25)Ti(0.75))O(3) ceramic was prepared by solid-state reaction. This material was characterized by x-ray diffraction and Fourier transform Raman spectroscopy. The temperature dependent dielectric properties were investigated in the frequency range from 1 kHz to 1 MHz. The dielectric measurements indicated a diffuse phase transition. The broadening of the dielectric permittivity in the frequency range as well as its shifting at higher temperatures indicated a relaxor-like behaviour for this material. The diffusivity and the relaxation strength were estimated using the modified Curie-Weiss law. The optical properties were analysed by ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL) measurements at room temperature. The UV-vis spectrum indicated that the Ba(Zr(0.25)Ti(0.75))O(3) ceramic has an optical band gap of 2.98 eV. A blue PL emission was observed for this compound when excited with 350 nm wavelength. The polarity as well as the PL property of this material was attributed to the presence of polar [TiO(6)] distorted clusters into a globally cubic matrix.

Comparative Histopathological Analysis of Human Pulps after Class I Cavity Preparation with a High-Speed Air-Turbine Handpiece or Er:YAG Laser

The purpose of this study was to comparatively evaluate the response of human pulps after cavity preparation with different devices. Deep class I cavities were prepared in sound mandibular premolars using either a high-speed air-turbine handpiece (Group 1) or an Er: YAG laser (Group 2). Following total acid etching and the application of an adhesive system, all cavities were restored with composite resin. Fifteen days after the clinical procedure, the teeth were extracted and processed for analysis under optical microscopy. In Group 1 in which the average for the remaining dentin thickness (RDT) between the cavity floor and the coronal pulp was 909.5 mu m, a discrete inflammatory response occurred in only one specimen with an RDT of 214 mu m. However, tissue disorganization occurred in most specimens. In Group 2 (average RDT = 935.2 mu m), the discrete inflammatory pulp response was observed in only one specimen (average RDT = 413 mu m). It may be concluded that the high-speed air-turbine handpiece caused greater structural alterations in the pulp, although without inducing inflammatory processes.

Dosimetric properties of UV irradiated calcium co-doped borate glass-ceramic

The thermoluminescence (TL) response of Dy and Li doped 20CaB(4)O(7)-80CaB(2)O(4) (Wt%) glass-ceramic irradiated with ultraviolet (UV) radiation was studied. In order to act as TL activator ions, the Dy and Li ions were included in the matrix during the melting process to increase its TL efficiency. A single crystalline CaB2O4 phase was present in the glass-ceramic as determined by X-ray diffraction (XRD). The glass-ceramic 20CaB(4)O(7)-80CaB(2)O(4):Dy,Li wt% (named 20CBO7:Dy,Li) is a newly prepared TL material. Its thermoluminescent dosimetric characteristics have shown a linear response under UV radiation exposure and a good TL signal reproducibility, thus proving to be a promising material for using as an ultraviolet radiation dosimeter. (C) 2007 Elsevier B.V. All rights reserved.

Phase-transition studies of Ba(0.90)Ca(0.10)(Ti(1-x)Zr(x))O(3) ferroelectric ceramic compounds

Perovskite-structured Ba(0.90)Ca(0.10)(Ti(1-x)Zr(x))O(3) ceramics were prepared in this work and subsequently studied in terms of composition-dependent dielectric and high-resolution long-range order structural properties from 30 to 450 K. The dielectric response of these materials was measured at several frequencies in the range from 1 kHz to 1 MHz. Combining both techniques, including Rietveld refinement of the X-ray diffraction data, allowed observing that, when increasing Zr(4+) content, the materials change from conventional to diffuse and relaxor ferroelectric compounds, the transition occurring spontaneously at the x = 0.18 composition. Interestingly, this spontaneous transition turned out to be prevented for a further increase of Zr(4+). On the basis of all the dielectric and structural results processed, a phase diagram of this system is presented. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Internal Residual Stress Measurements in a Bioactive Glass-Ceramic Using Vickers Indentation

The residual stress distribution that arises in the glass matrix during cooling of a partially crystallized 17.2Na(2)O-32.1CaO-48.1SiO(2)-2.5P(2)O(5) (mol%) bioactive glass-ceramic was measured using the Vickers indentation method proposed by Zeng and Rowcliffe (ZR). The magnitude of the determined residual stress at the crystal/glass boundary was 1/4-1/3 of the values measured using X-ray diffraction (within the crystals) and calculated using Selsing`s model. A correction for the crack geometry factor, assuming a semi-elliptical shape, is proposed and then good agreement between experimental and theoretical values is found. Thus, if the actual crack geometry is taken into account, the indentation technique of ZR can be successfully used. In addition, a numerical model for the calculation of residual stresses that takes into account the hemispherical shape of the crystalline precipitates at a free surface was developed. The result is that near the sample surface, the radial component of the residual stress is increased by 70% in comparison with the residual stress calculated by Selsing`s model.

Cr3+ and Cr4+ luminescence in glass ceramic silica

This paper reports on the effect of glass ceramic silica matrix on [CrO4](4-) and Cr2O3 NIR and visible luminescence. Chromium-containing silica was obtained by precipitation from water-glass and chromium nitrate acid solution with thermal treatment at 1000 degrees C. From XRD results silica and silica-chromium samples are crystalline. The chromium emission spectrum presents two main broad bands: one in the NIR region (1.1-1.7 mu m) and other in the visible region (0.6-0.7 mu m) assigned to Cr4+ and to Cr3+, respectively. This thermal treated glass ceramic silica-chromium sample stabilizes the [CrO4](4-) where Cr4+ substitutes for Si4+ and also hexacoordinated Cr3+ group probably as segregated phase in the system. It can be pointed out that luminescence spectroscopy is a powerful toot for detecting the two chromium optical centers in the glass ceramic silica. (C) 2008 Elsevier B.V. All rights reserved.

Spin contamination in XOO radicals X = F, Cl, Br, HO: How is the investigation of the HOOO radical affected

We have analysed the effect of spin contamination in the wavefunction of HOOO. At least, two solutions can be found for the HF wavefunction. One, lower in energy, presents a high spin contamination and gives qualitatively incorrect structural parameters. On the other hand, the less contaminated HF reference gives structural parameters that are in better agreement with experiment, and positive spin densities on all atoms. Some of the problems described during previous investigations of HOOO can now be traced to problems in the HF reference. For the first time we report a CCSD(T) estimation of the structure of HOOO cis employing a HF reference with small spin contamination. (C) 2008 Elsevier B.V. All rights reserved.

Estudo microscópico do reparo ósseo na mandíbula de ratos submetida a ostectomias a fresa cirúrgica e laser de Er:YAG

Proposição: avaliar histologicamente o reparo ósseo, especialmente a velocidade de cicatrização, após ostectomias a fresa cirúrgica e a laser de Er:YAG, sem contato, em diferentes intensidades de energia, in vivo. Materiais e método: 20 ratos (Novergicus Cepa Wistar), divididos em cinco grupos de quatro animais, foram submetidos a ostectomias da cortical óssea do corpo mandibular a fresa cirúrgica e a laser de Er:YAG (400 mJ/6 Hz), sem contato, no lado direito; no lado esquerdo foram realizadas ostectomias a laser de Er:YAG nas intensidades de 350 mJ/6 Hz e 300 mJ/6 Hz, sem contato. O laser foi aplicado sob irrigação constante. Foi utilizada matriz metálica para padronização das cavidades. Os tempos cirúrgicos foram sete, 14, 45, 60 e 90 dias pós-operatórios, e os espécimens analisados ao microscópio óptico. Resultados: as ostectomias a fresa cirúrgica apresentaram reparo ósseo a partir do endósteo cortical e do trabeculado remanescente. Aos 45 dias, observou-se o restabelecimento cortical, e após remodelação óssea. O reparo ósseo após irradiação a laser apresentou neoformação óssea a partir da superfície externa e endósteo corticais. Áreas de dano térmico foram verificadas nas três condições de irradiação, limitando-se a superfície. Estas áreas não foram mais evidenciadas aos 60 dias pós-operatórios. Neste período e adiante, verificou-se remodelação óssea. Conclusão: o reparo ósseo após ostectomias a laser de Er:YAG ocorreu através de corredores de cicatrização. O reparo ósseo após ostectomias a fresa cirúrgica tende a forma centrífuga. Já o reparo ósseo após irradiação a laser de Er:YAG tende a forma centrípeta. A velocidade de reparo foi maior nas ostectomias a fresa cirúrgica do que nas ostectomias a laser. Aos 90 dias, verificou-se reparo ósseo comparativamente homogêneo nas quatro condições propostas.

Extração com CO2 supercrítico de óleos essenciais de Hon-sho e Ho-sho : experimentos e modelagem

Uma das tecnologias que mais avançou nas últimas décadas, como uma alternativa para as tradicionais técnicas de extração de produtos naturais, é a técnica de Extração com Fluidos Supercríticos. A extração com fluidos supercríticos destacase entre os processos industriais de extração pela qualidade dos produtos obtidos e por não causar danos ambientais quando usa dióxido de carbono (CO2) no estado supercrítico como solvente. Este trabalho teve como objetivo a realização de experimentos de extração de óleos essenciais com dióxido de carbono no estado supercrítico de folhas de duas variedades da árvore Canforeira (Cinnamomum camphor Ness & Eberm.) conhecidas como Hon-sho e Ho-sho, a fim de determinar as melhores condições operacionais de processo. Os óleos essenciais obtidos destas plantas têm importância econômica devido aos seus principais componentes: linalol e cânfora. Os melhores parâmetros de extração obtidos, quando se consideram os rendimentos de óleo essencial, foram os seguintes: vazão de CO2 = 2 mL/min, temperatura = 50°C, pressão = 90 bar e diâmetro de partícula = 0,1 mm. Outro objetivo foi a obtenção das curvas de extração: Rendimento de óleo essencial versus Tempo de extração, adequando, a partir dos dados experimentais, alguns modelos matemáticos encontrados na literatura para descrever o comportamento destas extrações. Dos modelos estudados o que melhor se adequou à extração de óleos essenciais de folhas foi o modelo proposto por Reverchon (1996), o qual proporcionou uma boa reprodutibilidade dos dados experimentais, mostrandose eficiente na representação de extração com fluidos supercríticos de óleos essenciais de Hon-sho e Ho-sho a partir de suas folhas.

Estudo Microscópico do reparo ósseo em alvéolos de ratos irradiados com laser de Er:YAG

Proposição: avaliar a aplicação da tecnologia laser de Er:YAG em tecido ósseo alveolar. Materiais e Método: estudo experimental in vivo, com a amostragem selecionada de forma aleatória, randomizada, com um grupo teste e outro controle. Constou de 20 ratos, da espécie Rattus novergicus albinus, cepa Wistar, machos, subdivididos em quatro grupos, correspondendo aos tempos experimentais de sete, 14, 21 e 45 dias. Todos os animais foram grupo teste no lado direito e controle do lado esquerdo. Foi avaliado o efeito do uso de três pulsos de laser de Er:YAG à energia de 500 mJ/pulso e freqüência de 2 Hz, conduzido por fibra ótica, no modo de entrega em contato, através da análise das fases histológicas do reparo ósseo após extração cirúrgica do primeiro molar superior dos ratos. Foram avaliadas a qualidade e a velocidade do reparo ósseo alveolar. Resultados: aos sete dias, observou-se intensa atividade osteoblástica no grupo teste. As trabéculas apresentaram-se dirigidas no sentido ascendente e convergente. Ao contrário, o grupo controle apresentou neoformação óssea somente aos 14 dias, com trabéculas em forma circunvolutiva e ascendente. Aos 14 dias no grupo teste e aos 21 dias no grupo controle, evidenciou-se semelhança na atividade osteoblástica-osteoclástica, em diferentes fases de neoformação e remodelação óssea. No grupo teste, aos 21 dias, encontrou-se tecido ósseo maduro. Aos 45 dias, ambos os grupos apresentaram-se com tecido ósseo lamelar maduro do tipo esponjoso. Conclusão: após o uso de laser de Er:YAG, nos parâmetros utilizados, não foram observadas áreas de ablação e necrose teciduais, em todos os tempos experimentais; o reparo ósseo alveolar após o uso de laser Er:YAG, nos parâmetros utilizados, ocorreu mais rapidamente em comparação ao controle, principalmente entre os sete e 21 dias pós-operatórios; não houve diferença no reparo ósseo alveolar final, aos 45 dias pós-operatórios, em relação ao controle; e o modelo de cirurgia experimental é válido para pesquisas futuras em reparo ósseo alveolar.

Yo-ho e uma garrafa de BUM!

Música componente do jogo “Musikinésia (http://www.loa.sead.ufscar.br/musikinesia.php)” desenvolvido pela equipe do Laboratório de Objetos de Aprendizagem da Universidade Federal de São Carlos (LOA/UFSCar).