Matter-wave two-dimensional solitons in crossed linear and nonlinear optical lattices

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Localization of collisionally inhomogeneous condensates in a bichromatic optical lattice

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Localization of a Bose-Fermi mixture in a bichromatic optical lattice

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Matter-wave localization in a weakly perturbed optical lattice

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Synthesis of (Ca,Nd)TiO3 powders by complex polymerization, Rietveld refinement and optical properties

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Extensive Comparisons of Optical Fast-OFDM and Conventional Optical OFDM for Local and Access Networks

A performance comparison between a recently proposed novel technique known as fast orthogonal frequency-division multiplexing (FOFDM) and conventional orthogonal frequency-division multiplexing (OFDM) is undertaken over unamplified, intensity-modulated, and direct-detected directly modulated laser-based optical signals. Key transceiver parameters, such as the maximum achievable transmission capacity and the digital-to-analog/analog-to-digital converter (DAC/ADC) effects are explored thoroughly. It is shown that, similarly to conventional OFDM, the least complex and bandwidth efficient FOFDM can support up to similar to 20 Gb/s over 500 m worst-case multimode fiber (MMF) links having 3 dB effective bandwidths of similar to 200 MHz X km. For compensation of the DAC/ADC roll-off, a power-loading (PL) algorithm is adopted, leading to an FOFDM system improvement of similar to 4 dB. FOFDM and conventional OFDM give similar optimum DAC/ADC parameters over 500 m worst-case MMF, while over 50 km single-mode fiber a maximum deviation of only similar to 1 dB in clipping ratio is observed due to the imperfect chromatic dispersion compensation caused by one-tap equalizers.

SrZrO3 powders obtained by chemical method: Synthesis, characterization and optical absorption behaviour

Strontium zirconate (SrZrO3) powders have been synthesized by the polymeric precursor method after heat treatment at different temperatures for 2 h in oxygen atmosphere. The decomposition of precursor powder was followed by thermogravimetric analysis, X-ray diffraction (XRD) and Fourier transform Raman (FT-Raman). The UV-vis absorption spectroscopy measurements suggested the presence of intermediary energy levels in the band gap of structurally disordered powders. XRD, Rietveld refinement and FT-Raman revealed that the powders are free of secondary phases and crystallizes in the orthorhombic structure. (C) 2007 Elsevier Masson SAS. All rights reserved.

Comparative study of Cr3C2-NiCr coatings obtained by HVOF and hard chromium coatings

In the present work the corrosion resistance of micro-cracked hard chromium and Cr3C2-NiCr (HVOF) coatings applied on a steel substrate have been compared using open-circuit potential (E-OC) measurements, electrochemical impedance spectroscopy (EIS) and polarization curves. The coatings surfaces and cross-section were characterized before and after corrosion tests using optical microscopy (OM) and scanning electron microscopy (SEM). After 18 h of immersion, the open-circuit potential values were around -0.50 and -0.25V/(Ag vertical bar AgCl vertical bar KClsat) for hard chromium and Cr3C2- NiCr, respectively. The surface analysis done after 12 h of immersion showed iron on the hard chromium surface inside/near surface cracks, while iron was not detected on the Cr3C2-NiCr surface even after 18 h. For longer immersion time hard chromium was more degraded than thermal sprayed coating. For hard chromium coating a total resistance values between 50 and 80 k Omega cm(2) were measured and two well-defined time constants were observed, without significant change with the immersion time. For Cr3C2-NiCr coating the total impedance diminished from around 750 to 25 k Omega cm(2) as the immersion time increased from 17 up to 132 h and two overlapped time constants were also observed. Polarization curves recorded after 18 h of immersion showed a lower current and higher corrosion potential for Cr3C2-NiCr coating than other samples studied. (c) 2005 Elsevier Ltd. All rights reserved.

Synthesis, characterization, structural refinement and optical absorption behavior of PbWO(4) powders

The present paper describes the synthesis, characterization, structural refinement and optical absorption behavior of lead tungstate (PbWO(4)) powders obtained by the complex polymerization method heat treated at different temperatures for 2h in air atmosphere. PbWO(4) powders were characterized by X-ray diffraction (XRD), Rietveld refinement, Fourier transform Raman (FT-Raman) spectroscopy and ultraviolet visible (UV-vis) absorption spectroscopy measurements. XRD, Rietveld refinement and FT-Raman revealed that PbWO(4) powders are free of secondary phases and crystallizes in a tetragonal structure. The UV-vis absorption spectroscopy measurements suggest the presence of intermediary energy levels into the band gap of structurally disordered powders. (C) 2008 Elsevier B.V. All rights reserved.

SnO2 nanocrystals synthesized by microwave-assisted hydrothermal method: towards a relationship between structural and optical properties

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

SrMoO4 powders processed in microwave-hydrothermal: Synthesis, characterization and optical properties

In this work, we report on the synthesis of SrMoO4 powders by co-precipitation method and processed in a microwave-hydrothermal at 413 K for 5 h. These powders were analyzed by X-ray diffraction (XRD), Fourier transform Raman (FT-Raman), ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL). XRD analyses revealed that the SrMoO4 powders are free of secondary phases and crystallize in a tetragonal structure. FT-Raman investigations showed the presence of Raman-active vibration modes correspondent for this molybdate. UV-vis technique was employed to determine the optical band gap of this material. SrMoO4 powders exhibit an intense PL emission at room temperature with maximum peak at 540 nm (green region) when excited by 488 nm wavelength of an argon ion laser. (C) 2007 Elsevier B.V. All rights reserved.

A Contribution to the Estimation of Binary Halide and Pseudo-Halide Equilibrium Constants using a Linear Extrapolation Methodology

The molar single ion activity coefficient (y(F)) of fluoride ions was determined at 25 degrees C and ionic strengths between 0.100 and 3.00 mol L(-1) NaClO(4) using an ion-selective electrode. The activity coefficient dependency on ionic strength was determined to be Phi(F) = log y(F) = 0.2315I-0.041I(2). The function Phi(F)(I), combined with functions obtained in previous work for copper (Phi(Cu)) and hydrogen (Phi(H)), allowed us to make the estimation of the stoichiometric and thermodynamic protonation constants of some halides and pseudo-halides as well as the formation constants of some pseudo-halides and fluoride 1:1 bivalent cation complexes. The calculation procedure proposed in this paper is consistent with critically-selected experimental data. It was demonstrated that it is possible to use Phi(F)(I) for predicting the thermodynamic equilibrium parameters independently of Pearson's hardness of acids and bases.

Changes in optical properties caused by UV-irradiation of aquatic humic substances from the amazon river basin: Seasonal variability evaluation

Aquatic humic substances (AHS) isolated from two characteristic seasons of the Negro river, winter and summer corresponding to floody and dry periods, were structurally characterized by (13)C nuclear magnetic ressonance. Subsequently, AHS aqueous solutions were irradiated with a polychromatic lamp (290-475 nm) and monitored by its total organic carbon (TOC) content, ultraviolet-visible (UV-vis) absorbance, fluorescence and Fourier transformed infrared spectroscopy (FTIR). As a result, a photobleaching upto 80% after irradiation of 48 h was observed. Conformational rearrangements and formation of low molecular complexity structures were formed during the irradiation, as deduced from the pH decrement and the fluorescence shifting to lower wavelengths. Additionally a significant mineralization with the formation of CO(2), CO, and inorganic carbon compounds was registered, as assumed by TOC losses of up to 70%. The differences in photodegradation between samples expressed by photobleaching efficiency were enhanced in the summer sample and related to its elevated aromatic content. Aromatic structures are assumed to have high autosensitization capacity effects mediated by the free radical generation from quinone and phenolic moieties.

Structural and optical properties of GdAlO3:RE3+ (RE = Eu or Tb) prepared by the Pechini method for application as X-ray phosphors

In this work, GdAlO3:RE3+ (RE = Eu or Tb) was successfully prepared by the Pechini method at lower temperatures when compared to others methods as solid-state synthesis and sol-gel process. In accordance to the XRD data, the fully crystalline single-phase GdAlO3 could be obtained at 900 degrees C. The differential thermal analysis (DTA) shows a crystallization peak at 850 degrees C. The samples are composed by monocrystalline particles (50-120 nm) exhibiting the formation of aggregates among them, which indicates the beginning of the sinterization process. This feature indicates a strong tendency to the formation of aggregates, which is a suitable ability for the close-packing of particles, and hence a potential application in X-ray intensifying screens. Luminescence measurements indicate Gd3+ -> RE3+ energy transfer. The Eu3+ emission spectra exhibit all the characteristics D-5(0) -> F-7(j) transitions and the observed profile suggests that RE3+ ions occupy at least one site without center of symmetry. For terbium-doped samples, the D-5(3) -> F-7(j) (blue emission) and D-5(4) -> F-7(j) (green emission) transitions were observed and the ratio between them may depend on the Tb3+ content due to cross-relaxation processes. (C) 2009 Elsevier B.V. All rights reserved.

New phosphinate ligand synthesis and its effect on optical properties of the europium beta-diketonate complex

The synthesis and characterization of a new organic ligand monooctyldiphenylphosphinate (L) is described, as well as a new Eu(3+) diketonate complex [Eu(tta)(3)(L)(2)] (tta = thenoyltrifluoracetone). The ligand (L) was formed by substitution reaction (80% yield) and characterized by uni- and bidimensional (1)H, (13)C and (31)P NMR experiments, to confirm its molecular structure. The coordination of (L) to Eu(3+) in the complex [Eu(tta)(3)(L)(2)] was confirmed by FT-IR spectra. The emission spectra present the same profile when excited in Eu(3+) or in the ligands, suggesting an energy transfer from ligands to Eu(3+) ions. The emission spectra of the precursor [Eu(tta)(3)(H(2)O)(2)], and [Eu(tta)(3)(L(2))] present bands arising from f-f intra-configurational transitions. The only (5)D(0)-(7)F(0) transition shows the presence of at least one site without symmetry center. The FWHM of such transition is 7 cm(-1) and 57 cm(-1) for [Eu(tta)(3)(H(2)O)(2)] and [Eu(tta)(3)(L)(2)] complexes, respectively. This widening is provided by the presence of large groups around Eu(3+) ion. The calculated intensity parameters Omega(2) and Omega(4) show that the interaction features between center-ion and ligand are different; the small value of Omega(4) is related to long range effects of alkyl chain. The Langmuir isotherms of this ligand and complex have been investigated although their hydrolysis in water subphase does not allow stable monolayers. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim