Correlative light-electron fractography of interlaminar fracture in a carbon-epoxy composite

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

Frequency measurements of CD3OH and (CH3OH)-C-13 optically pumped far-infrared laser lines

We report the frequency measurements of 18 optically pumped far-infrared (FIR) laser lines generated from CD3OH and (CH3OH)-C-13. We use the heterodyne technique of mixing FIR laser radiations and microwave radiation on a metal-insulator-metal point-contact tunnel diode to determine the FIR laser frequencies. Two FIR laser systems, consisting of CO2 waveguide pump lasers and Fabry-Perot FIR laser cavities, were used as optical sources. (C) 1997 Optical Society of America.

Book Review of Twilight of the Mammoths: Ice Age Extinctions and the Rewilding of America</i> by Paul S. Martin

Applying ecological studies to the adaptations of prehistoric human hunter-gatherer groups has greatly increased our abilities to interpret effects of an ever-changing environment and our access to critical resources on these populations. The Pleistocene/Holocene transition, its climate and human genesis in the new world, draws intensive interest from a number of scientific communities. In Twilight of the Mammoths, Paul Martin adds his views, which are of no surprise, on the megafaunal extirpations during a cultural period referred to in North America as Clovis.

Persistent luminescence behavior of materials doped with Eu2+ and Tb3+

In this work, the persistent luminescence mechanisms of Tb3+ (in CdSiO3) and Eu2+ (in BaAl2O4) based on solid experimental data are compared. The photoluminescence spectroscopy shows the different nature of the inter- and intraconfigurational transitions for Eu2+ and Tb3+, respectively. The electron is the charge carrier in both mechanisms, implying the presence of electron acceptor defects. The preliminary structural analysis shows a free space in CdSiO3 able to accommodate interstitial oxide ions needed by charge compensation during the initial preparation. The subsequent annealing removes this oxide leaving behind an electron trap. Despite the low band gap energy for CdSiO3, determined with synchrotron radiation UV-VUV excitation spectroscopy of Tb3+, the persistent luminescence from Tb3+ is observed only with UV irradiation. The need of high excitation energy is due to the position of F-7(6) level deep below the bottom of the conduction band, as determined with the 4f(8)-> 4f(7)5d(1) and the ligand-to-metal charge-transfer transitions. Finally, the persistent luminescence mechanisms are constructed and, despite the differences, the mechanisms for Tb3+ and Eu2+ proved to be rather similar. This similarity confirms the solidity of the interpretation of experimental data for the Eu2+ doped persistent luminescence materials and encourages the use of similar models for other persistent luminescence materials. (C) 2012 Optical Society of America

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

Polarization effect on the two-photon absorption of a chiral compound

In this report, we investigate the polarization effect (linear, elliptical and circular) on the two-photon absorption (2PA) properties of a chiral compound based in azoaromatic moieties using the femtosecond Z-scan technique with low repetition rate and low pulse energy. We observed a strong 2PA modulation between 800 nm and 960 nm as a function the polarization changes from linear through elliptical to circular. Such results were interpreted employing the sum-over-essential states approach, which allowed us to model the 2PA circular-linear dichroism effect and to identifier the overlapping of the excited electronic states responsible by the 2PA allowed band. (C) 2012 Optical Society of America

Invariant Solutions of Richards' Equation for Water Movement in Dissimilar Soils

Scaling methods allow a single solution to Richards' equation (RE) to suffice for numerous specific cases of water flow in unsaturated soils. During the past half-century, many such methods were developed for similar soils. In this paper, a new method is proposed for scaling RE for a wide range of dissimilar soils. Exponential-power (EP) functions are used to reduce the dependence of the scaled RE on the soil hydraulic properties. To evaluate the proposed method, the scaled RE was solved numerically considering two test cases: infiltration into relatively dry soils having initially uniform water content distributions, and gravity-dominant drainage occurring from initially wet soil profiles. Although the results for four texturally different soils ranging from sand to heavy clay (adopted from the UNSODA database) showed that the scaled solution were invariant for a wide range of flow conditions, slight deviations were observed when the soil profile was initially wet in the infiltration case or deeply wet in the drainage case. The invariance of the scaled RE makes it possible to generalize a single solution of RE to many dissimilar soils and conditions. Such a procedure reduces the numerical calculations and provides additional opportunities for solving the highly nonlinear RE for unsaturated water flow in soils.

Generation of copper nanoparticles induced by fs-laser irradiation in borosilicate glass

Glasses containing metallic nanoparticles are promising materials for technological applications in optics and photonics. Although several methods are available to generate nanoparticles in glass, only femtosecond lasers allow controlling it three-dimensionally. In this direction, the present work investigates the generation of copper nanoparticles on the surface and in the bulk of a borosilicate glass by fs-laser irradiation. We verified the formation of copper nanoparticles, after heat treatment, by UV-Vis absorption, transmission electron microscopy and electron diffraction. A preferential growth of copper nanoparticles was observed in the bottom of the irradiated region, which was attributed to self-focusing in the glass. (c) 2012 Optical Society of America

Femtosecond laser induced synthesis of Au nanoparticles mediated by chitosan

This paper reports the synthesis of Au nanoparticles by 30-fs pulses irradiation of a sample containing HAuCl4 and chitosan, a biopolymer used as reducing agent and stabilizer. We observed that it is a multi-photon induced process, with a threshold irradiance of 3.8 x 10(11) W/cm(2) at 790 nm. By transmission electron microscopy we observed nanoparticles from 8 to 50 nm with distinct shapes. Infrared spectroscopy indicated that the reduction of gold and consequent production of nanoparticles is related to the fs-pulse induced oxidation of hydroxyl to carbonyl groups in chitosan. (C) 2011 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

Research Training Program: Duke University and Brazilian Society of Cardiology

Background: Research coaching program focuses on the development of abilities and scientific reasoning. For health professionals, it may be useful to increase both the number and quality of projects and manuscripts. Objective: To evaluate the initial results and implementation methodology of the Research and Innovation Coaching Program of the Research on Research group of Duke University in the Brazilian Society of Cardiology. Methods: The program works on two bases: training and coaching. Training is done online and addresses contents on research ideas, literature search, scientific writing and statistics. After training, coaching favors the establishment of a collaboration between researchers and centers by means of a network of contacts. The present study describes the implementation and initial results in reference to the years 2011-2012. Results: In 2011, 24 centers received training, which consisted of online meetings, study and practice of the contents addressed. In January 2012, a new format was implemented with the objective of reaching more researchers. In six months, 52 researchers were allocated. In all, 20 manuscripts were published and 49 more were written and await submission and/or publication. Additionally, five research funding proposals have been elaborated. Conclusion: The number of manuscripts and funding proposals achieved the objectives initially proposed. However, the main results of this type of initiative should be measured in the long term, because the consolidation of the national production of high-quality research is a virtuous cycle that feeds itself back and expands over time. (Arq Bras Cardiol 2012;99(6):1075-1081)

Indirect doping of microstructures fabricated by two-photon polymerization with gold nanoparticles

Nanoplasmonics and metamaterials sciences are rapidly growing due to their contributions to photonic devices fabrication with applications ranging from biomedicine to photovoltaic cells. Noble metal nanoparticles incorporated into polymer matrix have great potential for such applications due to their distinctive optical properties. However, methods to indirectly incorporate metal nanoparticles into polymeric microstructures are still on demand. Here we report on the fabrication of two-photon polymerized microstructures doped with gold nanoparticles through an indirect doping process, so they do not interfere in the two-photon polymerization (2PP) process. Such microstructures present a strong emission, arising from gold nanoparticles fluorescence. The microstructures produced are potential candidates for nanoplasmonics and metamaterials devices applications and the nanoparticles production method can be applied in many samples, heated simultaneously, opening the possibility for large scale processes. (C) 2012 Optical Society of America

Analysis of dispersive and dissipative media with optical resonances

In this paper we analyze the problem of light-matter interaction when absorptive resonances are imbedded in the material dispersion. We apply an improved approach to aluminum (Al) in the optical frequency range to investigate the impact of these resonances on the operating characteristics of Al-based nanoscale devices. Quantities such as group velocity, stored energy density, and energy velocity, normally obtained using a single resonance model [Wave Propagation and Group Velocity (Academic Press, 1960), Nat. Mater. 11, 208 (2012)], are now accurately calculated regardless of the medium adopted. We adapt the Loudon approach [Nat. Mater. 11, 208 (2012)] to media with several optical resonances and present the details of the extended model. We also show pertinent results for Al-based metal-dielectric-metal (MDM) waveguides, around spectral resonances. The model delineated here can be applied readily to any metal accurately characterized by Drude-Lorentz spectral resonance features. (C) 2012 Optical Society of America