Resonant excitation of Mn local vibrational modes in the higher order Raman spectra of nanocrystalline Ga(1-x)Mn(x)N films

The effect of manganese on the vibrational properties of Ga(1-x)Mn(x)N (0 <= x <= 0.18) films has been investigated by Raman scattering using 488.0 and 632.8 nm photon excitations. The first-order transverse and longitudinal optical GaN vibrational bands were observed in the whole composition range using both excitations, while the corresponding overtones, as well as a prominent peak located in 1238 cm(-1) (153.5 meV) were only observed in the Mn-containing films under 488.0 nm excitation. We propose that the peak observed at 1238 cm(-1) is due to resonant Mn local vibrational modes, the excitation process being related to electronic transitions involving the Mn acceptor band.

Local Er(III) environment in luminescent titanosilicates prepared from microporous precursors

The local environment of Er3+ ions in microporous titanosilicate ETS-10 and in synthetic narsarsukite and glassy materials obtained by calcination of ETS-10 has been investigated by EXAFS, Raman and photoluminescence spectroscopies. Er L-III-edge EXAFS studies of Er3+-doped ETS-10 support the view that the exchanged Er3+ ions reside close to the (negatively charged) TiO6 octahedra. In ETS-10, Er3+ is partially bonded to framework oxygen atoms and hydration water molecules. The Er...Ti distance (3.3 Angstrom) is similar to the Na...Ti distances (3.15-3.20 Angstrom) reported previously for Na-ETS-10. Although the exact location of the ErO6 units within the host structure of Er3+-doped synthetic narsarsukite is still an open question, it is most likely that Er3+ substitutes Ti4+ rather than Na+ ions. EXAFS spectroscopy indicates that no significant clustering of erbium atoms occurs in the titanosilicate samples studied. Evidence for the insertion of Er3+ ions in the framework of narsarsukite has been obtained by Raman spectroscopy. This is indicated by the increasing full-width at half-maximum (FWHM) of the 775 cm(-1) peak and the increasing intensity of the anatase peaks as the erbium content increases. In addition, as the narsarsukite Er3+ content increases a band at ca. 515 cm(-1) firstly broadens and subsequently a new peak appears at ca. 507 cm(-1).Er3+-doped narsarsukite exhibits a characteristic local vibrational frequency, (h) over bar omega ca. 330 cm(-1), with an electron-phonon coupling, g ca. 0.2, which constitutes additional evidence for framework Er3+ insertion. The number of lines in the infrared emission spectrum of synthetic narsarsukite indicates the presence of two optically-active erbium centres with very similar local environments and an average I-4(13/2) lifetime of 7.8 +/- 0.2 ms.

Thermally stimulated crystallization glass system of (20-x)LiO2-80TeO(2)-xWO(3)

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

EU-3+ AND GD-3+ SPECTROSCOPY IN FLUOROINDATE GLASSES

Luminescence data for Eu3+ and Gd3+ in fluoroindate glasses are compared to those of a fluorozirconate glass. Emission is observed from Eu3+ 5D(J) (J = 0, 1, 2 and 3) and Gd3+ P-6(7/2) excited-state levels and the results put in evidence Eu-Eu and Gd-Eu energy transfer processes. Vibronic bands related to a 320 cm-1 vibrational mode could be observed for Eu3+ luminescent transitions with DELTAJ = 0, 1 and 2 and also for the P-6(7/2) --> S-8(7/2) transition of Gd3+. Lanthanide ion site symmetry is closer to an inversion center in fluoroindate glasses than it is in fluorozirconate.

The Holstein-Anderson impurity model

A Holstein-Anderson impurity model is presented. Both the electronic states and the vibrational mode associated to the impurity are treated within a novel 'entangled' effective medium approach (a non-perturbative, self-consistent method). Vibronic spectra and susceptibilities are readily computed for the symmetric, half-filled case. As expected, charge fluctuations (electron-phonon interactions) depletes the magnetic response (susceptibility) when compared to the no-phonon case. © 2001 Published by Elsevier Science B.V.

Estudo dos difenilfosfinatos de lantânio ativados por cério, európio e térbio emissores luminescentes multicores

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Structural and vibrational study of cubic Sb2O3 under high pressure

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Local order of Pb1-xLaxZr0.40Ti 0.60O3 ferroelectric ceramic materials probed by X-ray absorption and Raman spectroscopies

This paper reports on the structural characterization of Pb 1-xLaxZr0.40Ti0.60O3 (PLZT) ferroelectric ceramic compositions prepared by the conventional solid state reaction method. X-ray absorption spectroscopy (XAS) and Raman spectroscopy were used to probe the local structure of PLZT samples that exhibits a normal and relaxor ferroelectric behavior. From the Zr K-edge and Pb LIII-edge EXAFS spectra, a considerable dissymmetry of Zr and Pb sites was observed in all samples, including those showing a long-range order cubic symmetry and a relaxor behavior. The Raman spectroscopy results confirmed the existence of a local disorder in all PLZT samples through the observation of Raman active vibrational modes. The variation in the intensity of the E(TO 3) mode in the PLZT relaxor samples indicates that the process of correlation between nanodomains stabilizes at temperatures lower than T m. © 2013 Elsevier B.V. All rights reserved.

Generalized duality between local vector theories in D=2+1

The existence of an interpolating master action does not guarantee the same spectrum for the interpolated dual theories. In the specific case of a generalized self-dual (GSD) model defined as the addition of the Maxwell term to the self-dual model in D = 2 + 1, previous master actions have furnished a dual gauge theory which is either nonlocal or contains a ghost mode. Here we show that by reducing the Maxwell term to first order by means of an auxiliary field we are able to define a master action which interpolates between the GSD model and a couple of non-interacting Maxwell-Chern-Simons theories of opposite helicities. The presence of an auxiliary field explains the doubling of fields in the dual gauge theory. A generalized duality transformation is defined and both models can be interpreted as self-dual models. Furthermore, it is shown how to obtain the gauge invariant correlators of the non-interacting MCS theories from the correlators of the self-dual field in the GSD model and vice-versa. The derivation of the non-interacting MCS theories from the GSD model, as presented here, works in the opposite direction of the soldering approach.

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.

Local and global magnetic properties of Zn1-xCoxO and Mn-doped GaAs thin films

Amorphous and crystalline thin films of Mn-doped(0.5%-10%) GaAs and crystalline thin films of Zn1-xCoxO(x = 3%-20%) were investigated by means of magnetic susceptibility and electron spin resonance (ESR). For the Mn-doped GaAs samples, our results show the absence of ferromagnetic ordering for the amorphous films in the 300 > T > 2 K temperature range, in contrast to the ferromagnetism found in crystalline films for T-C < 110 K. A single ESR line with a temperature independent g-value (g similar to 2) is observed for the amorphous films, and the behavior of this ESR linewidth depends on the level of crystallinity of the film. For the Mn-doped GaAs crystalline films, only a ferromagnetic mode is observed for T < TC when the film is ferromagnetic. Turning now the Zn1-xCoxO films, ferromagnetic loops were observed at room temperature for these films. The magnetization data show an increasing of the saturation magnetization M. as a function of x reaching a maximum value for x approximate to 10%. ESR experiments at T = 300 K in the same films show a strong anisotropic ferromagnetic mode (FMR) for x = 0.10.

The Mode of Action of Recombinant Mycobacterium tuberculosis Shikimate Kinase: Kinetics and Thermodynamics Analyses

Tuberculosis remains as one of the main cause of mortality worldwide due to a single infectious agent, Mycobacterium tuberculosis. The aroK-encoded M. tuberculosis Shikimate Kinase (MtSK), shown to be essential for survival of bacilli, catalyzes the phosphoryl transfer from ATP to the carbon-3 hydroxyl group of shikimate (SKH), yielding shikimate-3-phosphate and ADP. Here we present purification to homogeneity, and oligomeric state determination of recombinant MtSK. Biochemical and biophysical data suggest that the chemical reaction catalyzed by monomeric MtSK follows a rapid-equilibrium random order of substrate binding, and ordered product release. Isothermal titration calorimetry (ITC) for binding of ligands to MtSK provided thermodynamic signatures of non-covalent interactions to each process. A comparison of steady-state kinetics parameters and equilibrium dissociation constant value determined by ITC showed that ATP binding does not increase the affinity of MtSK for SKH. We suggest that MtSK would more appropriately be described as an aroL-encoded type II shikimate kinase. Our manuscript also gives thermodynamic description of SKH binding to MtSK and data for the number of protons exchanged during this bimolecular interaction. The negative value for the change in constant pressure heat capacity (ΔCp) and molecular homology model building suggest a pronounced contribution of desolvation of non-polar groups upon binary complex formation. Thermodynamic parameters were deconvoluted into hydrophobic and vibrational contributions upon MtSK:SKH binary complex formation. Data for the number of protons exchanged during this bimolecular interaction are interpreted in light of a structural model to try to propose the likely amino acid side chains that are the proton donors to bulk solvent following MtSK:SKH complex formation. © 2013 Rosado et al.

On the influence of the mode-shapes of a marine propulsion shafting system on the prediction of torsional stresses

Torsional vibration predictions and measurements of a marine propulsion system, which has both damping and a highly flexible coupling, are presented in this paper. Using the conventional approach to stress prediction in the shafting system, the numerical predictions and the experimental torsional vibration stress curves in some parts of the shafting system are found to be quite different. The free torsional vibration characteristics and forced torsional vibration response of the system are analyzed in detail to investigate this phenomenon. It is found that the second to fourth natural modes of the shafting system have significant local deformation. This results in large torsional resonant responses in different sections of the system corresponding to different engine speeds. The results show that when there is significant local deformation in the shafting system for different modes, then multi-point measurements should be made, rather than the conventional method of using a single measurement at the free end of the shaft, to obtain the full torsional vibration characteristics of the shafting system.

Analysis of follicular events in owl monkeys (Aotus azarai infulatus) using B-mode and Doppler ultrasound

Ultrasound (B-mode) was used to analyze follicular events in 12 trained female owl monkeys (Aotus azarai infulatus). The animals were examined every 48 hours for over 90days to measure and map follicular growth in both ovaries and to measure (using Doppler velocimetry) local hemodynamic changes during the peri-ovulatory stage. There were 44 follicular growth events, each with two or three follicular waves, and a mean ± SEM interval between events of 17 ± 1.13 days. There were various hemodynamic changes during follicular growth; both vascular resistance index and pulsatility index decreased during the time when the follicle diameter peaked. Thus, both B-mode and Doppler ultrasound were useful for monitoring ovarian follicular events in owl monkeys. © 2013 Elsevier Inc.

A formação de professores de ensino técnico de nível médio estadual e suas relações com o Arranjo Produtivo Local na cidade de Jahu

Pós-graduação em Educação - FFC