In this study glass-ceramics were produced from vermiculite, a clay mineral found in abundance in the Northeast of Brazil. These materials were characterized by X-ray fluorescence, X-ray diffraction, the Vickers microhardness test and scanning electron microscopy. Chemical analysis revealed the material contains a wide variety of metal oxides which are potentiators of crystal formation in glass-ceramics. XRD patterns indicating sodium aluminosilicates as the main crystalline phase in all the samples treated at 750 degrees C. Scanning electron microscope (SEM) images show crystalline regions in all the samples.

We investigate the excitonic properties of a core-multishell semiconductor nanowire with type-II band mismatch, i.e. with spatially separated electrons and holes, under an external magnetic field. Our results demonstrate that, depending on the core wire radius, the carrier in the type-II band exhibits either a quantum dot-like or a quantum ring-like energy spectrum, corresponding to a carrier confinement in the core wire or in the outer shell, respectively. In the latter, a shell-to-core confinement transition can be induced by increasing the magnetic field intensity, which may lead to interesting photocurrent properties of these confining structures, tunable by the external field.

The effect of eccentricity distortions of core–multishell quantum wires on their electron, hole and exciton states is theoretically investigated. Within the effective mass approximation, the Schrödinger equation is numerically solved for electrons and holes in systems with single and double radial heterostructures, and the exciton binding energy is calculated by means of a variational approach. We show that the energy spectrum of a core–multishell heterostructure with eccentricity distortions, as well as its magnetic field dependence, are very sensitive to the direction of an externally applied electric field, an effect that can be used to identify the eccentricity of the system. For a double heterostructure, the eccentricities of the inner and outer shells play an important role on the excitonic binding energy, especially in the presence of external magnetic fields, and lead to drastic modifications in the oscillator strength.

Using the effective mass approximation, we present a theoretical study of surface roughness effects on electron energies in semiconductor quantum dots, which are demonstrated to increase up to approximately 6%

This work presents a theoretical study of the energy spectrum of GaAs/AlGaAs concentric double quantum rings, under an applied magnetic field directed perpendicular to the ring plane. The Schrodinger equation for this system is solved in a realistic model consisting of rings with finite barrier potentials. Numerical results show that increasing the magnetic field intensity leads to oscillations in the ground state energy which, in contrast to the usual Aharonov-Bohm oscillations, do not have a well defined period, due to the coupling between inner and outer rings states. However, when one considers an elliptical geometry for the rings, the energy spectra of the inner and outer ring states are decoupled and the periodicity of the oscillations is recovered.

The electron energy spectrum of GaAs/Al0.30Ga0.70As quantum rings under applied magnetic fields is calculated, taking into account the existence of rough interfaces between materials. The Schrödinger equation, within the effective mass approximation, is solved in a realistic model, not limited to small perturbations. Our numerical results show that the existence of roughness on the ring surface modifies significantly the electron confinement energy, lifts the degeneracy of the electron angular momentum transition points of the Aharonov–Bohm oscillations, and in some special cases, it can even suppress the ground state energy oscillations.

Thin ceramic powders of zinc aluminate ZnAl2O4 co-doped with Er3+ and Yb3+ were prepared by a combustion reaction and characterized from the spectroscopic point of view, with the aim of investigating the effect and mechanisms of upconversion emissions. The characteristic cubic spinel structure was predominantly formed for all doped samples, and intense upconversion emission was observed in the green and red spectral regions, under 980 nm diode laser excitation. The upconversion mechanism of both emissions was confirmed to involve two photon absorptions and it was found that the efficiencies of the emissions are considerably enhanced by increasing the Yb3+ concentration in relation to Er3+. The results indicate the potential of ZnAl2O4:Er3+, Yb3+ phosphor powders for applications in luminescent display panels and other photonic devices.

The exciton properties of Si∕Si1−xGex quantum wells (QWs) are investigated within a variational approach, taking into account interface effects for two possibilities of the band alignment, type I and type II. For the latter, two-dimensional (2D) and three-dimensional (3D) variational wave functions are used in order to give a better description of the exciton confinement, where a large enhancement on the exciton binding energy (about 30% for a 70 Å well width) is found for the 3D case. The effects due to the presence of external electromagnetic fields on exciton energies are also analyzed. Our theoretical results explain the exciton energy blueshifts recently found in photoluminescence experiments for type-I Si∕Si0.82Ge0.18 QWs when electric fields are applied in the growth direction. Exciton energy shifts due to magnetic fields are calculated, and a comparison between such shifts in the 2D and 3D approaches is performed for type-II wells. Numerical results show that interfacial layers of 15 Å thickness for a type-I (type-II) Si∕Si0.82Ge0.18 (Si0.70Ge0.30) QW lead to a variation of about 20 meV (25 meV) in relation to the abrupt well for a 50 Å well width, yielding a blueshift on the exciton total energy.

This work presents a theoretical study of the excitonic properties of Si1-xGex cylindrical quantum wires surrounded by a Si matrix, considering two possibilities for the conduction band alignment, type I and type II. The effect of nonabrupt interfaces between these materials on the exciton energies is investigated: an interfacial region of 15 angstrom in a 50 angstrom wide Si0.85Ge0.15(Si0.7Ge0.3) type-I (type-II) quantum wire leads to an exciton energy blueshift of the order of 10 meV. The excitonic behavior under an applied magnetic field parallel to the wire axis is also studied: exciton energies in type-I wires are weakly affected, while for type-II wires, increasing the field causes the electron angular momentum to change almost periodically, giving rise to Aharonov-Bohm oscillations of the exciton ground state energy.

Titanatos de chumbo dopados com itérbio e ítrio, PYbT e PYT foram preparados pelo método Pechini. Os materiais obtidos foram calcinados sobre fluxo de oxigênio em diferentes temperaturas e investigados utilizando-se as técnicas de difração de raios X (DRX), microscopia eletrônica de varredura (MEV) e espectroscopia na região do infravermelho (IV). O comportamento térmico de PbTiO3 dopados com itérbio e ítrio é descrito através de curvas termogravimétricas (TG) e análise térmica diferencial (ATD). Os resultados revelaram que a fase perovskita foi obtida em uma baixa temperatura e que o aumento da dopagem favorece a estabilidade térmica dos materiais obtidos.

The electrical properties of polycrystalline Si1−xGex∕HfO2∕Si metal-oxide-semiconductor (MOS) devices are investigated theoretically by solving self-consistently the Poisson and Schrödinger equations. Our calculations demonstrate that the combination of HfO2 as dielectric film and polycrystalline gates causes charge inversion in both substrate and gate layer for ultrathin oxide layers. This effect is a consequence of the high dielectric constant of HfO2, and it is expected to occur for all high-κ-based polygated MOS devices. However, the relative doping concentration between polycrystalline gate and substrate can be used to decrease the effect of gate inversion.

In this work, we will discuss Si-/SiGe and high-k oxides nanostructures. The exciton properties of strained Si/Si1-xGex quantum well (QW) are calculated taking into account interface effects and both possibilities of the band lineup of the conduction-band offset, type-I and type-II. Our numerical results show that interface fluctuations of only 10 A in a Si/Si1-xGex 50 A type-I QW (type-II QW) leads to a 25 meV (10 meV) blueshift of the exciton (transition) energy. Concerning high- k nanostructures, our simulation was performed in order to analyse how the charge image effects can modify the electronics properties in Si/HfO2 and Si/SrTiO3 based quantum wells. The results of Si/SrTiO3 (Si/HfO2) quantum wells indicate a recombination emission difference, as compared with the case when no charge image effects are included, of the order of 1.5 eV (0.7 eV).

Titanatos de chumbo dopados com itérbio e ítrio, PYbT e PYT foram preparados pelo método Pechini. Os materiais obtidos foram calcinados sobre fluxo de oxigênio em diferentes temperaturas e investigados utilizando-se as técnicas de difração de raios X (DRX), microscopia eletrônica de varredura (MEV) e espectroscopia na região do infravermelho (IV). O comportamento térmico de PbTiO3 dopados com itérbio e ítrio é descrito através de curvas termogravimétricas (TG) e análise térmica diferencial (ATD). Os resultados revelaram que a fase perovskita foi obtida em uma baixa temperatura e que o aumento da dopagem favorece a estabilidade térmica dos materiais obtidos.Rare earth modified lead titanate ceramics, PYbT and PYT, were prepared by the Pechini method. The materials were calcined under flowing oxygen at different temperatures and were investigated using X-ray diffraction, scanning electron microscopy and infrared spectroscopy. The thermal behavior of Ytterbium (Yb) and Yttrium (Y) modified PbTiO3 using thermogravimetric analysis and differencial thermal analysis are reported. The results revealed that the perovskite phase was obtained at low temperature and that the thermal stability of the materials is favored through dopant increase.

The exciton properties of Si/Si1-xGex strained quantum wells (QW's) are calculated taking into account interface and strain effects. Our numerical results allow us to conclude that interface fluctuations of only 10 angstrom in a type-I (type-II) strained Si/Si0.8Ge0.2 (Si/Si0.7Ge0.3) 50 angstrom QW leads to a 25 meV (10 meV) blueshift of the exciton energy. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

BACKGROUND:Depression is treated by a great variety of antidepressant treatments. SSRIs (such as fluoxetine) are well known: it is, however, sure that further progress is needed and the search for antidepressants with other mechanisms of action (such as tianeptine) or different efficacy is still of interest.METHODS:A multinational study compared tianeptine with fluoxetine in 387 patients with Depressive Episode, or Recurrent Depressive Disorder, or Bipolar Affective Disorder (ICD-10), in a double-blind parallel group design. They were treated for six weeks.RESULTS:At inclusion, no significant difference between groups was shown. Final MADRS scores were 15.7 and 15.8 with tianeptine and fluoxetine, respectively (ITT population) (p = 0.944). MADRS responders were 58% and 56% with tianeptine and fluoxetine, respectively (p = 0.710). No statistical difference was observed for the other efficacy parameters. Thirty-six withdrawals occurred in each group, without any difference for the reasons of discontinuation. There was no major difference between groups for the other safety parameters.CONCLUSIONS:In this study, both tianeptine and fluoxetine exhibited a good efficacy and safety.

A very large cervical tumor that extended to the upper mediastinum was seen in a newborn after an uneventful pregnancy. The computed axial tomography scan confirmed the presence of a solid mass with precise limits and scattered foci of calcifications situated in the anterolateral region of the neck. The infant underwent thyroidectomy on the seventh day after birth. Pathological examination revealed a follicular carcinoma of the thyroid and probable dyshormonogenetic hyperplastic goiter. At 5 months of age, whole body scans indicated the presence of lung and bone metastases, which were treated with therapeutic doses of radioiodine. Genomic DNA was obtained from the newborn, her parents, her paternal aunt, and her paternal grandparents. Denaturing gradient gel electrophoresis analysis of PCR fragments corresponding to exon 14 of the thyroid peroxidase (TPO) gene indicated the presence of a mutant TPO allele present in the propositus, her father, and her paternal grandmother. Sequencing of the TPO gene demonstrated a mutation resulting from an insertion of a single extra cytosine in a stretch of seven cytosines at positions 2505-2511. The insertion caused a frame shift and a stop signal in exon 16. This sequence would translate into a structurally modified and probably inactive TPO protein. We conclude that the aggressive thyroid metastatic carcinoma arose from a dyshormonogenetic goiter caused by a defective TPO protein.

The efficacy and safely of tianeptine were compared, in the course of a multicentre randomised, double-blind, parallel group study, to those of placebo in the treatment of Major Depressions and Bipolar Disorder, Depressed with or without melancholia, without psychotic features. After a I-week run-in placebo period, 126 depressed out-patients presenting DSM-III-R Major Depression or Bipolar Disorder, Depressed, with a total MADRS score of at least 25, were treated for 42 days with either tianeptine (25-50 mg/day) or placebo. Efficacy assessments were MADRS, CGI, HARS, Zung Depression Self Rating Scale and a VAS. Better efficacy of tianeptine was shown, and confirmed by covariance analyses, in final MADRS scores of the intention-to-treat population, of patients treated for at least 14 days and of completers; also in CGI items 1 and 2, MADRS item 10, and VAS. The results confirmed the efficacy of tianeptine (mean dosage: 37.5 mg/day) in the treatment of Major Depression and Bipolar Disorder, Depressed, with or without melancholia, compared to placebo. Tianeptine's acceptability did not differ from that of placebo. For adverse events, a higher incidence of headaches was found with tianeptine.