RAFT-mediated emulsion polymerization of styrene using a non-ionic surfactant

We report the successful RAFT-mediated emulsion polymerization of styrene using a non-ionic surfactant (Brij98), the highly reactive 1-phenylethyl phenyldithioacetate (PEPDTA) RAFT agent, and water-soluble initiator ammonium persulfate (APS). The molar ratio of RAFT agent to APS was identical in all experiments. Most of the monomer was contained within the micelles, analogous to microemulsion or miniemulsion systems but without the need of shear, sonication, cosurfactant, or a hydrophobe. The number-average molecular weight increased with conversion and the polydispersity index was below 1.2. This ideal 'living' behavior was only found when molecular weights of 9000 and below were targeted. It was postulated that the rapid transportation of RAFT agent from the monomer swollen micelles to the growing particles was fast on the polymerization timescale, and most if not all the RAFT agent is consumed within the first 10% conversion. In addition, it was postulated that the high nucleation rate from the high rate of exit ( of the R radical from the RAFT agent) and high entry rate from water-phase radicals ( high APS concentration) reduced the effects of 'superswelling' and therefore a similar molar ratio of RAFT agent to monomer was maintained in all growing particles. The high polydispersity indexes found when targeting molecular weights greater than 9000 were postulated to be due to the lower nucleation rate from the lower weight fractions of both APS and RAFT agent. In these cases, 'superswelling' played a dominant role leading to a heterogeneous distribution of RAFT to monomer ratios among the particles nucleated at different times.

A CONSTRUÇÃO DISCURSIVA DA IMAGEM DA ORGANIZAÇÃO PÚBLICA EM UM CONTEXTO REGIONAL POLÍTICO: O caso da UFABC

Esta pesquisa aborda como se constrói a imagem de uma instituição por meio dos discursos elaborados pela organização e pela imprensa nacional e regional. Estuda também os elementos macros que podem influenciar esta construção, em especial quando a organização está instalada em um contexto regional com forte apelo político. Além disso, reflete sobre a responsabilidade social da imprensa na construção da imagem organizacional. Para isso, foi realizada uma discussão procurando alinhar a prática à teoria, perpassando por temas como comunicação pública, o discurso das organizações e a imprensa na construção da imagem, e também a análise de case específico, o da Universidade Federal do ABC. Realizou-se também uma Observação Participante, visto que a pesquisadora está inserida no objeto pesquisado. Esta pesquisa propõe uma contribuição, em especial, aos profissionais e pesquisadores da comunicação pública, ao avaliar em que grau pode ser percebida uma influência política na construção da imagem organizacional das instituições públicas. Foi realizada uma análise com o objetivo de observar como a Universidade, que em 2013 completou sete anos de atividades, está sendo percebida e trabalhada pela imprensa e como se deu a influência do contexto político nos discursos midiáticos. Esse levantamento foi elaborado por meio da análise de conteúdo do clipping impresso e online da instituição, para identificar tendências gerais de interesse da mídia por segmentos e temas. Nesta análise, foi possível verificar uma clara relação entre o número de matérias consideradas negativas e o número de matérias com citações políticas, com referência ao ex-presidente Lula ou ao PT. Os períodos em que a universidade foi abordada pela imprensa por questões como alto índice de evasão e atraso das obras, foram também os períodos em que houve um aumento significativo nas citações político-partidárias. Por fim, foi realizada a análise de discurso em reportagens e artigos selecionados, que confrontaram a imagem trabalhada institucionalmente com a repercutida nos meios de comunicação. Este trabalho possibilitou verificar que nos anos analisados, em especial no ano de 2010, o discurso da organização foi construído mais com o objetivo de reverter a imagem negativa da imprensa do que construir a sua própria imagem.

Direct femtosecond laser inscription in transparent dielectrics

Since 1996 direct femtosecond inscription in transparent dielectrics has become the subject of intensive research. This enabling technology significantly expands the technological boundaries for direct fabrication of 3D structures in a wide variety of materials. It allows modification of non-photosensitive materials, which opens the door to numerous practical applications. In this work we explored the direct femtosecond inscription of waveguides and demonstrated at least one order of magnitude enhancement in the most critical parameter - the induced contrast of the refractive index in a standard borosilicate optical glass. A record high induced refractive contrast of 2.5×10-2 is demonstrated. The waveguides fabricated possess one of the lowest losses, approaching level of Fresnel reflection losses at the glassair interface. High refractive index contrast allows the fabrication of curvilinear waveguides with low bend losses. We also demonstrated the optimisation of the inscription regimes in BK7 glass over a broad range of experimental parameters and observed a counter-intuitive increase of the induced refractive index contrast with increasing translation speed of a sample. Examples of inscription in a number of transparent dielectrics hosts using high repetition rate fs laser system (both glasses and crystals) are also presented. Sub-wavelength scale periodic inscription inside any material often demands supercritical propagation regimes, when pulse peak power is more than the critical power for selffocusing, sometimes several times higher than the critical power. For a sub-critical regime, when the pulse peak power is less than the critical power for self-focusing, we derive analytic expressions for Gaussian beam focusing in the presence of Kerr non-linearity as well as for a number of other beam shapes commonly used in experiments, including astigmatic and ring-shaped ones. In the part devoted to the fabrication of periodic structures, we report on recent development of our point-by-point method, demonstrating the shortest periodic perturbation created in the bulk of a pure fused silica sample, by using third harmonics (? =267 nm) of fundamental laser frequency (? =800 nm) and 1 kHz femtosecond laser system. To overcome the fundamental limitations of the point-by-point method we suggested and experimentally demonstrated the micro-holographic inscription method, which is based on using the combination of a diffractive optical element and standard micro-objectives. Sub-500 nm periodic structures with a much higher aspect ratio were demonstrated. From the applications point of view, we demonstrate examples of photonics devices by direct femtosecond fabrication method, including various vectorial bend-sensors fabricated in standard optical fibres, as well as a highly birefringent long-period gratings by direct modulation method. To address the intrinsic limitations of femtosecond inscription at very shallow depths we suggested the hybrid mask-less lithography method. The method is based on precision ablation of a thin metal layer deposited on the surface of the sample to create a mask. After that an ion-exchange process in the melt of Ag-containing salts allows quick and low-cost fabrication of shallow waveguides and other components of integrated optics. This approach covers the gap in direct fs inscription of shallow waveguide. Perspectives and future developments of direct femtosecond micro-fabrication are also discussed.

ICA for watermarking digital images

A domain independent ICA-based approach to watermarking is presented. This approach can be used on images, music or video to embed either a robust or fragile watermark. In the case of robust watermarking, the method shows high information rate and robustness against malicious and non-malicious attacks, while keeping a low induced distortion. The fragile watermarking scheme, on the other hand, shows high sensitivity to tampering attempts while keeping the requirement for high information rate and low distortion. The improved performance is achieved by employing a set of statistically independent sources (the independent components) as the feature space and principled statistical decoding methods. The performance of the suggested method is compared to other state of the art approaches. The paper focuses on applying the method to digitized images although the same approach can be used for other media, such as music or video.