Solitons in atomic condensates, with optical lattices and field-induced dipole moments

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

Wide localized solutions of the parity-time-symmetric nonautonomous nonlinear Schrodinger equation

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

The modification of structural and optical properties of nano- and submicron ZnO powders by variation of solvothermal syntheses conditions

Nano- (30-60 nm) and submicron (100-350 nm) ZnO particles were synthesized using solvothermal method at 200 degrees C from an ethanolic solution of zinc acetate dihydrate, applying different reaction conditions, i.e., pH value of precursor and time of the reaction. The X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), UV-vis diffuse reflectance (DR), Raman spectroscopy, and photoluminescence (PL) spectroscopy have been employed for characterization of synthesized ZnO powders. It was shown that the structural, morphological, and optical properties are largely determined by reaction conditions during solvothermal synthesis. The particle crystallinity improves with the decrease of pH value and/or the increase of time of the reaction. The Raman and PL spectra analyses indicate that the oxygen interstitials are dominant intrinsic defects in solvothermally synthesized ZnO powders. It was observed that concentration of defects in wurtzite ZnO crystal lattices slightly changes with the variation of pH value of the precursor and time of the solvothermal reaction. The correlation between structural ordering and defect structure of particles and corresponding growth processes was discussed.

Synthesis and characterization of nanostructured TiO2-SnO2 composite

Nanostructured composites based on titanium dioxide have been studied in order to improve optical and photo-catalytic properties, as well as their performance in gas sensors. In this work, titanium and tin dioxides were simultaneously synthesized by the polyol method resulting in TiO2 platelet coated with SnO2 nanoparticles as was observed by scanning electron microscopy. The thermal analysis showed that the combined synthesis promotes more easily the crystallization of the TiO2 rutile phase. The composite obtained after heat treatment at 500 degrees C showed to be formed of almost only rutile phases of both oxides. The optical properties analyzed by UV-Vis spectroscopy showed that the combined oxides have higher absorbance, which reinforces a model found in the literature based on the flow of photo-generated electrons to the conduction band of SnO2 delaying the recombination of charges.

Characterization of grazing bifurcation in airfoils with control surface freeplay nonlinearity

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

Synthesis and characterization of nanostructured TiO2-SnO2 composite

Nanostructured composites based on titanium dioxide have been studied in order to improve optical and photo-catalytic properties, as well as their performance in gas sensors. In this work, titanium and tin dioxides were simultaneously synthesized by the polyol method resulting in TiO2 platelet coated with SnO2 nanoparticles as was observed by scanning electron microscopy. The thermal analysis showed that the combined synthesis promotes more easily the crystallization of the TiO2 rutile phase. The composite obtained after heat treatment at 500 °C showed to be formed of almost only rutile phases of both oxides. The optical properties analyzed by UV-Vis spectroscopy showed that the combined oxides have higher absorbance, which reinforces a model found in the literature based on the flow of photo-generated electrons to the conduction band of SnO2 delaying the recombination of charges.

Optimizing Amplifier Placements in a Multiwavelength Optical LAN/MAN: The Unequally Powered Wavelengths Case

Optical networks based on passive-star couplers and employing WDM have been proposed for deployment in local and metropolitan areas. These networks suffer from splitting, coupling, and attenuation losses. Since there is an upper bound on transmitter power and a lower bound on receiver sensitivity, optical amplifiers are usually required to compensate for the power losses mentioned above. Due to the high cost of amplifiers, it is desirable to minimize their total number in the network. However, an optical amplifier has constraints on the maximum gain and the maximum output power it can supply; thus, optical amplifier placement becomes a challenging problem. In fact, the general problem of minimizing the total amplifier count is a mixed-integer nonlinear problem. Previous studies have attacked the amplifier-placement problem by adding the “artificial” constraint that all wavelengths, which are present at a particular point in a fiber, be at the same power level. This constraint simplifies the problem into a solvable mixed integer linear program. Unfortunately, this artificial constraint can miss feasible solutions that have a lower amplifier count but do not have the equally powered wavelengths constraint. In this paper, we present a method to solve the minimum amplifier- placement problem, while avoiding the equally powered wavelength constraint. We demonstrate that, by allowing signals to operate at different power levels, our method can reduce the number of amplifiers required.

Routing and Wavelength Assignment (RWA) with Power Considerations In All- Optical Wavelength-Routed Networks

Routing and wavelength assignment (RWA) is an important problem that arises in wavelength division multiplexed (WDM) optical networks. Previous studies have solved many variations of this problem under the assumption of perfect conditions regarding the power of a signal. In this paper, we investigate this problem while allowing for degradation of routed signals by components such as taps, multiplexers, and fiber links. We assume that optical amplifiers are preplaced. We investigate the problem of routing the maximum number of connections while maintaining proper power levels. The problem is formulated as a mixed-integer nonlinear program and two-phase hybrid solution approaches employing two different heuristics are developed

Growth and Characterization of Silicon Carbide Thin Films Using a Nontraditional Hollow Cathode Sputtering Technique

Silicon carbide (SiC) is considered a suitable candidate for high-power, high-frequency devices due to its wide bandgap, high breakdown field, and high electron mobility. It also has the unique ability to synthesize graphene on its surface by subliming Si during an annealing stage. The deposition of SiC is most often carried out using chemical vapor deposition (CVD) techniques, but little research has been explored with respect to the sputtering of SiC. Investigations of the thin film depositions of SiC from pulse sputtering a hollow cathode SiC target are presented. Although there are many different polytypes of SiC, techniques are discussed that were used to identify the film polytype on both 4H-SiC substrates and Si substrates. Results are presented about the ability to incorporate Ge into the growing SiC films for the purpose of creating a possible heterojunction device with pure SiC. Efforts to synthesize graphene on these films are introduced and reasons for the inability to create it are discussed. Analysis mainly includes crystallographic and morphological studies about the deposited films and their quality using x-ray diffraction (XRD), reflection high energy electron diffraction (RHEED), transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), Auger electron spectroscopy (AES) and Raman spectroscopy. Optical and electrical properties are also discussed via ellipsometric modeling and resistivity measurements. The general interpretation of these analytical experiments indicates that the films are not single crystal. However, the majority of the films, which proved to be the 3C-SiC polytype, were grown in a highly ordered and highly textured manner on both (111) and (110) Si substrates.

Development and characterization of light-emitting diodes (LEDs) based on ruthenium complex single layer for transparent displays

In this work, two ruthenium complexes, [Ru(bpy)(3)](PF6)(2) and [Ru(ph2phcn)(3)](PF6)(2) in poly(inethylinethacrylate) matrix were employed to build single-layer light-emitting electrochemical cells by spin coating on indium tin oxide substrate. In both cases the electroluminescence spectra exhibit a relatively broad band with maxima near to 625 rim and CIE (x, y) color coordinates of (0.64, 0.36), which are comparable with the photoluminescence data in the same medium. The best result was obtained with the [Ru(bpy)(3)](PF6)(2) device where the optical output power approaches 10 mu W at the band maximum with a wall-plug efficiency higher than 0.03%. The lowest driving voltage is about 4 V for an electrical current of 20 mA. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Analysis, manufacture and characterization of Ni/Cu functionally graded structures

In this work, an experimental and numerical analysis and characterization of functionally graded structures (FGSs) is developed. Nickel (Ni) and copper (Cu) materials are used as basic materials in the numerical modeling and experimental characterization. For modeling, a MATLAB finite element code is developed, which allows simulation of harmonic and modal analysis considering the graded finite element formulation. For experimental characterization, Ni-Cu FGSs are manufactured by using spark plasma sintering technique. Hardness and Young's modulus are found by using microindentation and ultrasonic measurements, respectively. The effective gradation of Ni/Cu FGS is addressed by means of optical microscopy, energy dispersive spectrometry, scanning electron microscopy and hardness testing. For the purpose of comparing modeling and experimental results, the hardness curve, along the gradation direction, is used for identifying the gradation profile; accordingly, the experimental hardness curve is used for approximating the Young's modulus variation and the graded finite element modeling is used for verification. For the first two resonance frequency values, a difference smaller than 1% between simulated and experimental results is obtained. (C) 2012 Elsevier Ltd. All rights reserved.

Investigation of the optical absorption of a magnetic colloid from the thermal to the electronic time-scale regime: measurement of the free-carrier absorption cross-section

The free-carrier absorption cross-section sigma of a magnetic colloid composed of magnetite nanoparticles dispersed in oil is obtained by using the Z-scan technique in different experimental conditions of the laser beam. We show that it is possible to obtain sigma with picosecond pulsed and millisecond chopped beams with pulse frequencies smaller than about 30 Hz. For higher pulse frequencies, the heating of the colloidal system triggers the appearance of the Soret effect. This effect artificially increases the value of sigma calculated from the experimental results. The limits of the different experimental setups are discussed. (C) 2012 Optical Society of America

Femtosecond third-order nonlinear spectra of lead-germanium oxide glasses containing silver nanoparticles

This work reports on the spectral dependence of both nonlinear refraction and absorption in lead-germanium oxide glasses (PbO-GeO2) containing silver nanoparticles. We have found that this material is suitable for all-optical switching at telecom wavelengths but at the visible range it behaves either as a saturable absorber or as an optical limiter. (C) 2012 Optical Society of America

Characterization of multiple reflections and phase space properties for a periodically corrugated waveguide

Dynamical properties for a beam light inside a sinusoidally corrugated waveguide are discussed in this paper. The beam is confined inside two-mirrors: one is flat and the other one is sinusoidally corrugated. The evolution of the system is described by the use of a two-dimensional and nonlinear mapping. The phase space of the system is of mixed type therefore exhibiting a large chaotic sea, periodic islands and invariant KAM curves. A careful discussion of the numerical method to solve the transcendental equations of the mapping is given. We characterize the probability of observing successive reflections of the light by the corrugated mirror and show that it is scaling invariant with respect to the amplitude of the corrugation. Average properties of the chaotic sea are also described by the use of scaling arguments.

Light scattering on the structural characterization of DMPG vesicles along the bilayer anomalous phase transition

Highly charged vesicles of the saturated anionic lipid dimyristoyl phosphatidylglycerol (DMPG) in low ionic strength medium exhibit a very peculiar thermo-structural behavior. Along a wide gel-fluid transition region, DMPG dispersions display several anomalous characteristics, like low turbidity, high electrical conductivity and viscosity. Here, static and dynamic light scattering (SLS and DLS) were used to characterize DMPG vesicles at different temperatures. Similar experiments were performed with the largely studied zwitterionic lipid dimyristoyl phosphatidylcholine (DMPC). SLS and DLS data yielded similar dimensions for DMPC vesicles at all studied temperatures. However, for DMPG, along the gel-fluid transition region, SLS indicated a threefold increase in the vesicle radius of gyration, whereas the hydrodynamic radius, as obtained from DLS, increased 30% only. Despite the anomalous increase in the radius of gyration, DMPG lipid vesicles maintain isotropy, since no light depolarization was detected. Hence, SLS data are interpreted regarding the presence of isotropic vesicles within the DMPG anomalous transition, but highly perforated vesicles, with large holes. DLS/SLS discrepancy along the DMPG transition region is discussed in terms of the interpretation of the Einstein-Stokes relation for porous vesicles. Therefore, SLS data are shown to be much more appropriate for measuring porous vesicle dimensions than the vesicle diffusion coefficient. The underlying nanoscopic process which leads to the opening of pores in charged DMPG bilayer is very intriguing and deserves further investigation. One could envisage biotechnological applications, with vesicles being produced to enlarge and perforate in a chosen temperature and/or pH value. (C) 2012 Elsevier Ireland Ltd. All rights reserved.