Interference effects in nonplanar wires with a two-dimensional electron gas

We have studied the universal conductance fluctuations (UCF) due to quantum interface in a two-dimensional electron gas (2DEG) grown on the substrates with pre-patterned, sub-micron wires. The dependence of UCF on the angle between the direction of the magnetic field and the substrate has been investigated. We found, that magnetoresistance traces for different angles are completely uncorrelated. A non-planar character of electron motion is responsible for these angular conductance fluctuations. We compared the experimental results with a simple geometrical model.

Wannier functions of a one-dimensional photonic crystal with inversion symmetry

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Electrodeposition of copper on titanium wires: Taguchi experimental design approach

Electrodeposition of thin copper layer was carried out on titanium wires in acidic sulphate bath. The influence of titanium surface preparation, cathodic current density, copper sulphate and sulphuric acid concentrations, electrical charge density and stirring of the solution on the adhesion of the electrodeposits was studied using the Taguchi statistical method. A L(16) orthogonal array with the six factors of control at two levels each and three interactions was employed. The analysis of variance of the mean adhesion response and signal-to-noise ratio showed the great influence of cathodic current density on adhesion. on the contrary, the other factors as well as the three investigated interactions revealed low or no significant effect. From this study optimized electrolysis conditions were defined. The copper electrocoating improved the electrical conductivity of the titanium wire. This shows that copper electrocoated titanium wires could be employed for both electrical purpose and mechanical reinforcement in superconducting magnets. (C) 2008 Elsevier B.V. All rights reserved.

Analysis in vitro of direct bonding system with cyanoacrylate ester and orthodontic wires

The aim of this study was to evaluate the tensile strength of orthodontic wires bonded onto the enamel with cyanoacrylate ester. To obtain the specimens, 120 human premolars (extracted for orthodontic or periodontal reasons) were included in acrylic blocks of rapid polymerization with three teeth each. Four groups were formed with ten specimens each. In the specimens, a dental splint model was made with cyanoacrylate ester and round stainless steel wire. In groups I, II and III, cyanoacrylate ester was used with round steel wires, with variation in diameter: 0.014 inches; 0.016 inches and 0.018 inches, respectively. In group IV, round steel wire 0.018 inches was used with photo polymerizing resin composite with previous acid etching. The adhesive force of the materials was measured in two points under the action of the tensiometer (ETM-USA). The number of loose wires was counted along with those that remained fixed according to the different levels of force applied because of the direction of the tensile force (vertical or horizontal) and the diameter of the wire used. The data obtained were first submitted to a descriptive analysis and then submitted to a statistical analysis (Friedman's Test and Dunn's Test of Multiple Comparison - Epi-info 3.2). Within the limitations of the experimental conditions presented, the cyanoacrylate ester or 'Super Bonder (R)' maintained bonded to enamel and steel wires (0.016 and 0.018 inches) during the tensile strength tests under different levels of applied forces.

Effect of heat treatment on stainless steel orthodontic wires

This study evaluated the effect of heat treatment on CrNi stainless steel orthodontic archwires. Half of forty archwires of each thickness - 0.014 (0.35 mm), 0.016 (0.40 mm), 0.018 (0.45 mm) and 0.020 (0.50 mm) (totalling 160 archwires) - were subjected to heat treatment while the remainder were not. All of the archwires had their individual thickness measured in the anterior and posterior regions using AutoCad 2000 software before and after compressive and tensile strength testing. The data was statistically analysed utilising multivariance ANOVA at a 5% significance level. All archwires without heat treatment that were subjected to tensile strength testing presented with anterior opening, which was more accentuated in the 0.020 archwires. In the posterior region, the opening produced by the tensile force was more accentuated in the archwires without heat treatment. There was greater stability in the thermally treated archwires, especially those subjected to tensile strength testing, which indicates that the heat treatment of orthodontic archwires establishes a favourable and indispensable condition to preserve the intercanine width.

Intersubband plasmon-phonon modes in quantum wires at high temperatures

Coupled intersubband plasmon-phonon modes are studied in a multisubband parabolic quantum wire at room temperatures. These modes are found by calculating the spectral weight function which is related to the inelastic Raman spectra. We use a 13 subband model. The plasmon-phonon coupling strongly modifies the dispersion relation of the intersubband modes in the vicinity of the optical phonon frequency omega(LO). Extra modes show up as a result of the electron-phonon interaction. We carefully study the density and temperature dependence of these extra modes. We also show that coupled intersubband plasmon-phonon modes should be observed for temperatures as high as 300 K.

1.5 mu m and visible up-conversion emissions in Er3+/Yb3+ co-doped tellurite glasses and optical fibers for photonic applications

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Fabrication and analysis of self-assembled photonic crystals structures

This paper presents the fabrication and analysis of a three-dimensional FCC photonic crystal (PhC) based on a self-assembly synthesis of monodispersive latex spheres. Experimental optical characterization, achieved by measurements of the specular reflectance under variable angles, indicated the clear presence of a Bragg diffraction pattern. Results are further explored by theoretical calculations based on the Finite Difference Time Domain (FDTD) method to determine the full PhC band structure.

Behavior of overhead transmission line parameters on the presence of ground-wires

Initially this paper shows the ground wire reduction process for generic multiphase transmission lines and after, the ground wire reduction process for a specilic 440-kV three-phase overhead transmission line. Following this, the influence of the ground wire reduction process considering two situations is shown: first, considering frequency independence and second, when these parameters are considered as frequency dependent. This paper presents analytical results for generic multiphase transmission lines. For a specific 440-kV three-phase overhead transmission line, analytical and graphic results are shown considering real data for every frequency between 10 Hz and 1 MHz.

Band-edge states of the zero(th)-order gap in quasi-periodic photonic superlattices

The photonic modes of Thue-Morse and Fibonacci lattices with generating layers A and B, of positive and negative indices of refraction, are calculated by the transfer-matrix technique. For Thue-Morse lattices, as well for periodic lattices with AB unit cell, the constructive interference of reflected waves, corresponding to the zero(th)-order gap, takes place when the optical paths in single layers A and B are commensurate. In contrast, for Fibonacci lattices of high order, the same phenomenon occurs when the ratio of those optical paths is close to the golden ratio. In the long wavelength limit, analytical expressions defining the edge frequencies of the zero(th) order gap are obtained for both quasi-periodic lattices. Furthermore, analytical expressions that define the gap edges around the zero(th) order gap are shown to correspond to the = 0 and = 0 conditions.

Active planar waveguides based on sol-gel Er3+-doped SiO2-ZrO2 for photonic applications: Morphological, structural and optical properties

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

PbO-GeO2 rib waveguides for photonic applications

This work presents for the first time to our knowledge the fabrication and characterization of rib waveguides produced with PbO-GeO2 (PGO) thin films. The target was manufactured using pure oxides ( 60 PbO-40 GeO2, in wt%) and amorphous thin films were produced with the RF sputtering technique. PGO thin films present small absorption in the visible and in the near infrared and refractive index of similar to 2.0. The definition of the rib waveguide structure was made using conventional optical lithography followed by plasma etching, performed in a Reactive Ion Etching (RIE) reactor. Light propagation mode in the waveguide structure was analyzed using integrated optic simulation software. Optical loss measurements were performed to determine the propagation loss at 633 nm, for ribs with height of 70 nm and width of 3-5 mu m; experimental values around 2 dB/cm were found for the propagation loss and confirmed the theoretical calculations. The results obtained demonstrate that PGO thin films are potential candidates for application in integrated optics. Published by Elsevier B.V.

Band edge states of the < n >=0 gap of Fibonacci photonic lattices

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Two-dimensional photonic crystals in antimony-based films fabricated by holography

In this work, we demonstrated the fabrication of two-dimensional (2D) photonic crystals layers (2D-PCLs) by combining holographic recording and the evaporation of antimony-based glasses. Such materials present high refractive indices that can be tuned from 1.8 to 2.4, depending on the film composition; thus, they are interesting dielectric materials for fabrication of 2D-PCLs. The good quality of the obtained samples allowed the measurement of their PC properties through the well-defined Fano resonances that appear in the transmittance spectrum measurements at different incidence angles. The experimental results are in good agreement with the calculated band diagram for the hexagonal asymmetric structure. (C) 2008 American Institute of Physics.