794 resultados para enhancement technologies
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Plasma processing of carbon fibers (CFs) is aimed to provide better contact and adhesion between individual plies without decrease in the CF mechanical resistance. This paper deals with surface modification of CFs by an atmospheric pressure dielectric barrier discharge (DBD) for enhancing the adhesion between the CF and the polymeric matrix. The scanning electron microscopy of the treated samples revealed many small particles distributed over entire surface of the fiber. These particles are product of the fiber surface etching during the DBD treatment that removes the epoxy layer covering as-received samples. The alteration of the CF surface morphology was also confirmed by the Atomic force microscopy (AFM), which indicated that the CF roughness increased as a result of the plasma treatment. The analysis of the surface chemical composition provided by X-ray photoelectron spectroscopy showed that oxygen and nitrogen atoms are incorporated onto the surface. The polar oxygen groups formed on the surface lead to the increasing of the CF surface energy. The results of interlaminar shear strength test (short beam) of CFs/polypropylene composites demonstrated a greater shear resistance of the composites made with CFs treated by DBD than the one with untreated fibers. Both the increase in surface roughness and the surface oxidation contribute for the enhancement of CF adhesion properties. © 2012 IEEE.
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Changing the sample's temperature from 200 K to 535 K, we observed 670-fold enhancement of a phonon-assisted upconversion emission at ≈754 nm obtained from a Nd3+-doped tellurite glass excited by 5 ns laser pulses at 805 nm. A rate-equation model, including the relevant energy levels and temperature dependent transition rates, is proposed to describe the process. The results fit well with the data when one considers the nonradiative transitions contributing for the 754 nm luminescence are promoted by an effective phonon mode with energy of 700 cm-1. © 2013 American Institute of Physics.
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Metallic nanoparticles (NPs) have been used to improve the sensibility of biosensors and bioassays either by enhancing radiative emission or inducing quenching process on fluorescent probes. The aim of this research was to study the interaction of silver and silver-pectin NPs with water-dispersed carboxyl-coated cadmium telluride (CdTe) quantum dots (QDs). Metallic NPs were observed to change the emission of these fluorophores through local field effects. In a solution-base platform, an increase of 82 % was observed for the CdTe emission due to the interaction of QDs and silver-pectin NPs. QDs interaction with silver NPs without pectin was also investigated and a smaller emission enhancement of 20 % was detected. We observed that the NPs' nature and QDs' surface charge and concentration are important parameters for NPs-QDs interaction. Moreover, the presence of the pectin polymer shows to be a key component to the observed fluorescence enhancement. © 2013 Springer Science+Business Media New York.
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