Exhumation of high-pressure granulites of the Guaxupe Complex, southeastern Brazil

This paper describes tectonic and metamorphic features of Precambrian rocks from the Guaxupe Complex and Varginha Shear Zone (VSZ) near the city of Guaxupe in the southern part of the Sao Francisco Craton, southeastern Brazil. The VSZ separates the metasediments of Araxa Group to the north from the granulites of Guaxupe Complex to the south. The sinistral transcurrent VSZ crosses the entire area striking approximately E-W, bending towards SE in the eastern part. Because of this bend, transpressional movement occurred, facilitating the exhumation of the garnet-rich rocks of the deepest exposed part of the granulite-facies terrane.In the garnet granulites the highest pressure-temperature conditions recorded are approximately 1040 degreesC and 14.4 kbar. The rocks underwent decompression from 14.0 kbar to 8.0 kbar, cooling from 980 degreesC to 710 degreesC, the retrograde path following the boundary between the kyanite and sillimanite stability fields. This interval is interpreted to record the uplift of the lower crustal granulite-facies terrane and re-equilibration during magmatic intrusions. For the felsic granulites an interval of 700-810 degreesC and 8.0-11.5 kbar was attained, also pointing to regional decompression.The granulites of the Guaxupe Complex comprise a medium- to high-pressure lower-crustal terrane, with local occurrences of higher-pressure garnet-rich gneisses, which were uplifted along a transpressional segment of the VSZ. Copyright (C) 2000 John Wiley & Sons, Ltd.

Hydrogen influence on gallium arsenide thin films prepared by rf-magnetron sputtering technique

We investigate the effect of the hydrogen intentional incorporation on the structural properties of the amorphous gallium arsenide prepared by rf-magnetron sputtering technique. The properties of the non-hydrogenated films are: band gap of 1.4 eV (E-04), Urbach energy of 110 meV, stoichiometric composition ([As]/[Ga] = 0.50), and dark conductivity of about 3.2 x 10(-5) (Omega.cm)(-1). Hydrogen was incorporated in the films by the introduction of an electronically controlled H-2 flux during deposition, keeping constant the other deposition parameters. It was observed that small hydrogen incorporation produces a great change in the structural properties of the films. The main changes result from the formation of GaAs nanocrystals with mean sizes of about 7 nm into the amorphous network.

Erbium-activated HfO2-based waveguides for photonics

Silica-based sol-gel waveguides activated by Er3+ ions are attractive materials for integrated optic devices. 70SiO(2)-30HfO(2) planar waveguides, doped with Er3+ concentrations ranging from 0.01 to 4 mol%, were prepared by sol-get route. The films were deposited on v-SiO2 and silica-on-silicon substrates, using dip-coating technique. The waveguides show a homogeneous surface morphology, high densification degree and uniform refractive index across the thickness. Emission in the C-telecommunication band was observed at room temperature for ill the samples upon excitation at 980 nm. The shape is found to be almost independent on erbium content, with a FWHM between 44 and 48 nm. The I-4(13/2) level decay curves presented a single-exponential profile, with a lifetime ranging between 1.1 and 6.7 ms, depending on the erbium concentration. The waveguide deposited on silica-on-silicon substrate supports one single propagation mode at 1.5 mum with a confinement coefficient of 0.85, and a losses of about 0.8 dB/cm at 632.8 nm. (C) 2003 Elsevier B.V. All rights reserved.

Phosphate functionalization of spongiolite surface

Spongiolite from Mato Grosso do Sul (Brazil), natural inorganic composite constituted of silica needles, was treated with concentrated phosphoric acid at high temperatures. Superficial coating of the needles was proved to be constituted of silicon diphosphate, a compound offering six-coordinated silicon sites. Owing to the affinity of three charged ions to phosphate groups, this coating acts as specific adsorbent for the rare earth elements which prefer octahedral coordination (starting from samarium, yttrium included). The uptake of lanthanum and neodymium are significantly lower due to different coordination tendencies. Lanthanide fixation upon silica with PO4 groups anchored on its surface may be useful in the manufacturing of special phosphate-silicate glasses. (C) 2003 Elsevier B.V. All rights reserved.

Upconversion luminescence in transparent glass ceramics containing beta-PbF2 nanocrystals doped with erbium

Frequency upconversion luminescence in erbium-doped PbGeO3-PbF2-CdF2-based transparent glass ceramics (TGC) under 980 nm infrared excitation is investigated. Upconversion emission signals around 410, 525, 550, 660, and 850 nm were generated and identified as due to the H-2(9/2) H-2(11/2), S-4(3/2), and F-4(9/2) transitions to the I-4(15/2) ground-state, and S-4(3/2)-I-4(13/2), respectively. The erbium ions excited-state emitting levels were populated via a combination of stepwise ground-state absorption (GSA), excited-state absorption (ESA), and cross-relaxation processes. The results also disclosed that both blue (410 nm) and red (660 nm) upconversion emission signals in the transparent glass ceramic sample presented twice as much intensity as compared to its vitreous counterpart. (C) 2003 Elsevier B.V. All rights reserved.

Remarks on infrared dynamics in QED(3)

In this work we study how the infrared sector of the interaction Hamiltonian can affect the construction of the S-matrix operator of QED in (2+1) dimensions.

Cytotoxic effects of cleansing solutions recommended for chemical lavage of pulp exposures

Purpose: To evaluate the in vitro cytotoxic effects of three cleansing solutions used for chemical lavage of pulp exposures. Materials and Methods: the immortalized odontoblast cell line (MDPC-23) was plated (30,000 cells/cm(2)) and incubated for 72 hrs in 24-well dishes. After counting the cell number under inverted light microscopy, 20 mul of the experimental and control solutions were added to 980 mul of fresh culture medium. Then, hydrogen peroxide (3%, H2O2), sodium hypochlorite (6%, NaOCl) or calcium hydroxide-saline solution (5g of Ca(OH)(2) in 10 mi of sterile distilled water) were added to wells for experimental Groups 1, 2 and 3, respectively. The positive and negative control groups received Syntac Sprint bonding agent (SS) and phosphate buffered saline (PBS), respectively. Following incubation for 120 min the cell number was counted again, the cell morphology was evaluated by scanning electron microscopy (SEM) and the cell metabolism was determined by the methyltetrazolium (MTT) assay. The scores obtained from cell counting and MTT assay were analyzed with an ANOVA followed by Fisher's PLSD tests. Results: H2O2 NaOCl solutions, and SS bonding agent were more cytotoxic than Ca(OH)2 or PBS. In the groups with H2O2 Or SS, only a few cells remained attached to the bottom of wells. The difference between these two groups was not statistically significant. H2O2, NaOCl and SS depressed the mitochondrial enzyme response by 97.7%, 97.3%, and 95.0%, respectively. on the other hand, Ca(OH)2 depressed the metabolic activity of cells by only 5%. While H2O2, NaOCl and SS caused extreme changes on the cell morphology, neither Ca(OH)2 nor PBS promoted dramatic changes in the cell morphology.

MULLER CELLS AND DIABETIC-RETINOPATHY

Muller cells provide nutrition for neural cells. We studied the structure and ultrastructure of Muller cells in the retina of thirty 3-month old Wistar rats; divided equally into 3 groups: normal rats, alloxan diabetic rats and treated alloxan diabetic rats. 1 and 12 months after induction of diabetes. We observed that the Muller cell nuclei under light microscope examination had hexagonal shape and higher density than the other nuclei. Differences between groups could be observed only by electron microscopy. In the diabetic rats, Muller cells presented dispersion of nuclear chromatin and electrondense nuclear granulations, with the presence of increased glycogen, dense bodies and lysosomes in the cytoplasm. The alterations were more frequent in the perivascular region and at 12 months. The treated diabetic rats exhibited some alterations we observed in diabetic rats. but these alterations were less intense. We conclude that, despite the treatment, the diabetic retinopathy continues to evolve.

Infrared-to-visible CW frequency upconversion in erbium activated silica-hafnia waveguides prepared by sol-gel route

70SiO(2)-30HfO(2) mol% planar waveguides, doped with Er3+ with concentrations ranging from 0.3 to 2 mol% were prepared by sol-gel route, using dip-coating deposition on vitreous-SiO2 substrates. Infrared-to-visible upconversion emission, upon excitation at 980 nm, has been observed for all the samples. The upconversion results in green, red and blue emissions. The investigation of the upconversion dynamic as a function of the Er3+ concentration and excitation power, show that processes such as excited state absorption and energy transfer upconversion are effective. (C) 2003 Elsevier B.V. All rights reserved.

Morphological and luminescent studies on nanosized Er, Yb-Yttrium oxide up-converter prepared from different precursors

In this paper, we report luminescent and morphological studies with yttrium oxide samples doped with ytterbium and erbium. The samples were prepared by the combustion method and also from different precursors: oxalate, basic carbonate and polymeric resin. All powders were identified Lis being an yttrium oxide with a C-form structure, independent of the employed precursor. From mean crystallite size measurements, it was verified that oxides prepared through the polymeric precursor and combustion methods lead to the smallest crystallite size. Particle shape and size were investigated by SEM and TEM, and showed that both the oxalate precursor and the combustion methods do not provide oxide materials of suitable shape or size, on the other hand. The basic carbonate and polymeric precursors resulted in spherically shaped particles with an average diameter of 90 and 15 run. respectively, Upon 980 run diode laser excitation, green and red emission lines were detected for all samples and were assigned to the H-2(11/2) S-4(3/2) -> I-4(15/2) and (4)Fg(9/2) -> 4I(15/12) transitions, respectively. Such transitions are characteristic for Er3+ and result from energy transfer from Yb3+ energy levels, F-2(7/2) -> F-2(5/2). A relationship between the decrease in the mean crystallite size and the enhancement in red emission was also established as well as the influence of the presence of a high percentage of Yb-3 Both factors promote ET from Yb3+ (F-2(5/2)) to Er3+ (I-4(11/2)). (c) 2004 Elsevier B.V. All rights reserved.

Evaluation of laser level populations of erbium-doped glasses

A simulation of erbium-doped glass systems, which provides population density for the excited states involved in the 1.5 mu m and also for 2.7 mu m emissions when pumped around 980 nm, is presented. To describe the diode pump laser processes, a theoretical model based in a coupled system of differential rate equations was developed. The approach used and the obtained spectroscopic parameters are discussed. The materials under study are two oxide glasses, lead fluoroborate (PbO-PbF2-B2O3), and heavy metal oxide (Bi2O3 PbO-Ga2O3) and a fluoride glass (ZrF4-BaF2-LaF3-AlF3-NaF), all of them doped with Er3+. (c) 2006 Elsevier B.V. All rights reserved.