Efeito na osseointegração de um novo método de nanotexturização de superfície de implantes através de anodização

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Excitation and damping of a self-modulated laser wakefield

Spatially, temporally, and angularly resolved collinear collective Thomson scattering was used to diagnose the excitation and damping of a relativistic-phase-velocity self-modulated laser wakefield. The excitation of the electron plasma wave was observed to be driven by Raman-type instabilities. The damping is believed to originate from both electron beam loading and modulational instability. The collective Thomson scattering of a probe pulse from the ion acoustic waves, resulting from modulational instability, allows us to measure the temporal evolution of the plasma temperature. The latter was found to be consistent with the damping of the electron plasma wave.

Photopatternable di-ureasil-zirconium oxocluster organic-inorganic hybrids as cost effective integrated optical substrates

Organic-inorganic hybrids containing methacrylic acid (McOH, CH(2)= C(CH(3))COOH)) modified zirconium tetrapropoxide, Zr(OPr(n))(4), classed as di-ureasil-zirconium oxo-cluster hybrids, have been prepared and structurally characterized by X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), Fourier transform infrared (FT-IR) and Raman (FT-Raman) spectroscopies, Si and C nuclear magnetic resonance (NMR), and atomic force microscopy (AFM). XRD and SAXS results have pointed out the presence of Si- and Zr-based nanobuilding blocks (NBBs) dispersed into the organic phase. Inter-NBBs correlation distances have been estimated for the pure di-ureasil and a model compound obtained. by hydrolysis/condensation of Zr(OPr(n))(4):McOH (molar ratio 1: 1): d(Si) approximate to 26 +/- 1 angstrom and d(Zr) approximate to 16 +/- 1 angstrom, respectively. In the case of the di-ureasil-zirconium oxo-cluster hybrids, these distances depend on the Zr relative molar percentage (rel. mol. Zr %) (d(Si) ranges from 18 to 25 angstrom and d(Zr) from 14 to 23 angstrom, as the rel. mol. Zr % increases from 5 to 75), suggesting that the Si- and Zr-based clusters are interconstrained. Complementary data from FT-IR, FT-Raman, (29)Si and (13)C NMR, and AFM support to a structural model where McOH-modified Zr-based NBBs (Zr-OMc) are present over the whole range of composition. At low Zr-OMc contents (rel. mol. Zr % <30) the clusters are well-dispersed within the di-ureasil host, whereas segregation occurs at the 0.1 mu m scale at high Zr-OMc concentration (rel. mol. Zr % = 50). No Zr-O-Si heterocondensation has been discerned. Monomode waveguides, diffractions gratings, and Fabry-Perot cavities have been written through the exposure of the hybrid monoliths to UV light. FT-Raman has shown that the chemical process that takes place under illumination is the polymerization of the methacrylate groups of the Zr-OMc NBBs. The guidance region in patterned channels is a Gaussian section located below the exposed surface with typical dimensions of 320 mu m wide and 88 mu m deep. The effective refractive index is 1.5162 (maximum index contrast on the order of 1 x 10(-4)) and the reflection coeficient of the Fabry-Perot cavity (formed by a grating patterned into a 0.278 cm channel) is 0.042 with a free spectral range value of 35.6 GHz.

What can light scattering spectroscopy do for membrane-active peptide studies

Highly charged peptides are important components of the immune system and belong to an important family of antibiotics. Although their therapeutic activity is known, most of the molecular level mechanisms are controversial. A wide variety of different approaches are usually applied to understand their mechanisms, but light scattering techniques are frequently overlooked. Yet, light scattering is a noninvasive technique that allows insights both on the peptide mechanism of action as well as on the development of new antibiotics. Dynamic light scattering (DLS) and static light scattering (SLS) are used to measure the aggregation process of lipid vesicles upon addition of peptides and molecular properties (shape, molecular weight). The high charge of these peptides allows electrostatic attraction toward charged lipid vesicles, which is studied by zeta potential (zeta-potential) measurements. Copyright (c) 2008 European Peptide Society and John Wiley & Sons, Ltd.

Raman and XRD study on brookite-anatase coexistence in cathodic electrosynthesized titania

Among the many methods developed for the synthesis of titanium dioxide, cathodic electrosynthesis has not received much attention because the resulting amorphous oxy-hydroxide matrix demands a further thermal annealing step to be transformed into crystalline titania. However, the possibility of filling deep recessed templates by the control of the solidliquid interface makes it a potentially suitable technique for the fabrication of porous scaffolds for photovoltaics and photocatalysis. Furthermore, a careful control of the crystallization process enables the growth of larger grains with lower density of grain boundaries, which act as electron traps that slow down electronic transport and promote charge recombination. In this report, well crystallized titania deposits were obtained by thermal annealing of amorphous deposits fabricated by cathodically assisted electrosynthesis on indium-tin oxide (ITO)substrates. The combined use of Raman spectroscopy and X-ray diffraction showed that the crystallization process is more intricate than previously assumed. It is shown that the amorphous matrix evolves into a rutile-free mixture of brookite and anatase at temperatures as low as 200 degrees C that persists up to 800 degrees C, when pure anatase dominates. The amount of brookite in the brookiteanatase mixture reaches a maximum at 400 degrees C. This very simple method for obtaining a brookiteanatase mixture and the ability to tune their proportions by thermal annealing is a promising alternative whose potential for solar cells and photocatalysis deserves a careful evaluation. Copyright (C) 2011 John Wiley & Sons, Ltd.

Effects of a CPT-even and Lorentz-violating nonminimal coupling on electron-positron scattering

We propose a new CPT-even and Lorentz-violating nonminimal coupling between fermions and Abelian gauge fields involving the CPT-even tensor (K-F)(mu nu alpha beta) of the standard model extension. We thus investigate its effects on the cross section of the electron-positron scattering by analyzing the process e(+) + e(-) -> mu(+) + mu(-). Such a study was performed for the parity-odd and parity-even nonbirefringent components of the Lorentz-violating (K-F)(mu nu alpha beta) tensor. Finally, by using experimental data available in the literature, we have imposed upper bounds as tight as 10(-12) (eV)(-1) on the magnitude of the CPT-even and Lorentz-violating parameters while nonminimally coupled. DOI: 10.1103/PhysRevD.86.125033

Lorentz violation bounds on Bhabha scattering

We investigate the effect of Lorentz-violating terms on Bhabha scattering in two distinct cases correspondent to vectorial and axial nonminimal couplings in quantum electrodynamics ( QED). In both cases, we find significant modifications with respect to the usual relativistic result. Our results reveal an anisotropy of the differential cross section which implies new constraints on the possible Lorentz-violating terms.

A graphical tool for an analytical approach of scattering photons by the Compton effect

The photons scattered by the Compton effect can be used to characterize the physical properties of a given sample due to the influence that the electron density exerts on the number of scattered photons. However, scattering measurements involve experimental and physical factors that must be carefully analyzed to predict uncertainty in the detection of Compton photons. This paper presents a method for the optimization of the geometrical parameters of an experimental arrangement for Compton scattering analysis, based on its relations with the energy and incident flux of the X-ray photons. In addition, the tool enables the statistical analysis of the information displayed and includes the coefficient of variation (CV) measurement for a comparative evaluation of the physical parameters of the model established for the simulation. (C) 2012 Elsevier B.V. All rights reserved.

Positron scattering from methane

We report on measurements of total cross sections for positron scattering from the fundamental organic molecule methane (CH(4)). The energy range of these measurements was 0.1-50 eV, whereas the energy resolution was similar to 100 meV when our Ni moderator was used and similar to 260 meV when the W moderator was employed. To assist us in interpreting these data, Schwinger multichannel calculations were performed at both static and static plus polarization levels of approximation for elastic positron scattering from 0.001 to 10 eV. These calculations are found to be in quite good qualitative agreement with our measured data, and they clearly educe the crucial role played by the target polarization in the low energy positron-CH(4) scattering dynamics.

Study of electron densities of normal and neoplastic human breast tissues by Compton scattering using synchrotron radiation

Electron densities of 33 samples of normal (adipose and fibroglangular) and neoplastic (benign and malignant) human breast tissues were determined through Compton scattering data using a mono-chromatic synchrotron radiation source and an energy dispersive detector. The area of Compton peaks was used to determine the electron densities of the samples. Adipose tissue exhibits the lowest values of electron density whereas malignant tissue the highest. The relationship with their histology was discussed. Comparison with previous results showed differences smaller than 4%. (C) 2012 Elsevier Ltd. All rights reserved.

Positron scattering from the cyclic ethers oxirane, 1,4-dioxane, and tetrahydropyran

In this paper we report original measurements of total cross sections (TCSs) for positron scattering from the cyclic ethers oxirane (C2H4O), 1,4-dioxane (C4H8O2), and tetrahydropyran (C5H10O). The present experiments focus on the low energy range from similar to 0.2 to 50 eV, with an energy resolution smaller than 300 meV. This study concludes our systematic investigation into TCSs for a class of organic compounds that can be thought of as sub-units or moieties to the nucleotides in living matter, and which as a consequence have become topical for scientists seeking to simulate particle tracks in matter. Note that as TCSs specify the mean free path between collisions in such simulations, they have enjoyed something of a recent renaissance in interest because of that application. For oxirane, we also report original Schwinger multichannel elastic integral cross section (ICS) calculations at the static and static plus polarisation levels, and with and without Born-closure that attempts to account for the permanent dipole moment of C2H4O. Those elastic ICSs are computed for the energy range 0.5-10 eV. To the best of our knowledge, there are no other experimental results or theoretical calculations against which we can compare the present positron TCSs. However, electron TCSs for oxirane (also known as ethylene oxide) and tetrahydropyran do currently exist in the literature and a comparison to them for each species will be presented. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3696378]

Effect of hydrogen bond formation on the elastic molecular scattering: a case study with methanol

Rayleigh optical activities of small hydrogen-bonded methanol clusters containing two to five molecules are reported. For the methanol trimer, tetramer, and pentamer both cyclic and linear structures are considered. After the geometry optimizations, the dipole moments and the dipole polarizabilities (mean, interaction, and anisotropic components) are calculated using HF, MP2 and DFT (B3LYP, B3P86 and BH&HLYP) with aug-cc-pVDZ extended basis set. The polarizabilities are used to analyse the depolarization ratios and the Rayleigh scattering activities. The variations in the activity and in the depolarization for Rayleigh scattered radiation with the increase in the cluster size for both cyclic and linear structures are analysed.

Interionic Interactions in Imidazolic Ionic Liquids Probed by Soft X-ray Absorption Spectroscopy

This work investigates pure ionic liquids (ILs) derived from an imidazolium ring with different carbonic chains and halides or bis(trifluoromethanesulfonilimide) (TFSI-) as anions, using X-ray absorption near edge spectroscopy (XANES) at different energies (N, S, O, F, and Cl edges) to probe the interionic interactions. XANES data show that the interaction with the anion is weaker when the cation is an imidazolium than when the salt is formed by smaller cations, as lithium, independently of the length of the carbonic chain attached to the imidazolium cation. The results also show that, for all studied as, it is not observed any influence of the anion on the XANES spectra of the cation, nor the opposite. 1-Methylimidazolium with Cl-, a small and strongly coordinating anion, presents in the N K XANES spectrum a splitting of the band corresponding to nitrogen in the imidazolic ring, indicating two different chemical environments. For this cation with TFSI-, on the contrary, this splitting was not observed, showing that the anion has a weaker interaction with the imidazolic ring, even without a lateral carbonic chain.

Changes in a nanoparticle's spectroscopic signal mediated by the local environment

Using a first-principles theoretical model the adsorption of a methyl radical on different sized silver nanoparticles is compared to the adsorption of the same radical on model surfaces. Calculations of our structural, dynamical and electronic properties indicated that small changes in the local environment will lead to small changes in infrared (IR) wavenumbers, but in dramatic changes in the IR signal. Our calculations indicate the lower the adsorption site coordination, the higher is the signal strength, suggesting that small changes in the electronic charge distribution will result in bigger changes in the polarizability and hence in the spectroscopic signal intensity. This effect explains, among others, the signal magnification observed for nanoparticles in surface enhanced Raman spectroscopic (SERS) experiments.

Continuous-wave watt-level Nd:YLF/KGW Raman laser operating at near-IR, yellow and lime-green wavelengths

A Nd:YLF/KGW Raman laser has been investigated in this work. We have demonstrated CW output powers at six different wavelengths, 1147 nm (0.70 W), 1163 nm (0.95 W), 549 nm (0.65 W), 552 nm (1.90 W), 573 nm (0.60 W) and 581 nm (1.10 W), with higher peak powers achieved under quasi-CW operation. Raman conversion of the 1053 nm fundamental emission is reported for the first time, enabling two new wavelengths in crystalline Raman lasers, 549 nm and 552 nm. The weak thermal lensing associated with Nd:YLF has enabled to achieve good beam quality, M-2 <= 2.0, and stable operation in relatively long cavities. (C) 2012 Optical Society of America