Repositório Institucional da Universidade de Aveiro
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A Double Click Strategy Applied to the Reversible Polymerization of Furan/Vegetable Oil Monomers
No full textThis investigation describes preliminary results related to the preparation of monomers based on vegetable oil derivatives bearing furan heterocycles appended through thiol-ene click chemistry, and their subsequent polymerization via the Diels-Alder (DA) polycondensation between furan and maleimide complementary moieties, i.e. a second type of click chemistry. Following the optimization of these interactions with model compounds, two basic approaches were considered for these DA polymerizations, namely (i) the use of monomers with two terminal furan rings in conjunction with bismaleimides (AA+BB systems) and (ii) the use of AB monomers incorporating both furan and maleimide end-groups. This ongoing study clearly showed that both approaches were successful, albeit with different outcomes, in terms of the nature of the products. The application of the retro-DA reaction confirmed their thermoreversible character, i.e. the clean-cut return to their respective starting monomers.FCTPOCI 2010REEQ/515/CTM/2005SFRH/BD/44884/200
Review of kinetic models for supercritical fluid extraction
No full textThe supercritical fluid extraction (SFE) of liquids and solid materials is gaining increasing interest and commercial application in last decades, most particularly under the recent concept of green chemistry and biorefinery. Hence, it is fundamental to provide adequate modeling of the SFE, in order to optimize operating conditions and simulate the global process. This work intends to review the most significant and physically sound models published in the literature for countercurrent liquid-supercritical fluid extraction and SFE of solid matrices, such as the linear driving force, shrinking core, broken and intact cells, and the combination of BIC and shrinking core models. The main assumptions and mass transfer expressions are presented and discussed. (C) 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.FP7/2007-2013CP-IP 228589-2 AFOR
Novel bacterial cellulose-acrylic resin nanocomposites
No full textThe preparation and characterization of new nanocomposite films based on two acrylic emulsions, composed of random copolymers of butyl acrylate and methyl methacrylate, and bacterial cellulose is reported. The new composite materials were obtained through a simple and green approach by casting water-based suspensions of the acrylic emulsions and bacterial cellulose nanofibrils. The excellent compatibility between these matrices and the natural reinforcing fibers, observed by scanning electron microscopy (SEM), was reflected in the enhanced thermal and mechanical properties of the ensuing composites. Thus, an increase of around 30 degrees C in the maximum degradation temperature was observed for a 10% content of bacterial cellulose. The new composites showed glass-rubber transition temperature profiles comparable to those of the pristine matrices, as shown by DMA, and increasing elastic moduli with increasing the bacterial cellulose content. The tensile tests revealed a substantial increase in Young's modulus and tensile strength and a corresponding decrease in elongation at break with increasing bacterial cellulose load. (C) 2010 Elsevier Ltd. All rights reserved.FCTSFRH/BPD/38515/2007National Program for Scientific re-equipmentRede/1509/RME/2005REEQ/515/CTM/200
Tratado de gloria
No full textEdição crítica de João Manuel Nunes Torrãotema da Glória é um tópico fundamental do renascimento europeu, herdado da Cultura Clássica. (...) O tratado De Gloria, de D. JErónimo Osório, publicado em 1549, em forma de diálogo, é constituído por cinco livros e visa debater uma das grandes questões que agitavam os humanistas no século XVI. Das 28 edições atestadas, em forma latina integral, treze foram publicadas até à morte do autor, o que revela bem a repercussão que teve no meio humanista europeu da época
PolyMeCo-An integrated environment for polygonal mesh analysis and comparison
No full textPolygonal meshes are used in several application areas to model different objects and structures. Depending on the application, mesh models sometimes have to be processed to, for instance, reduce their complexity (mesh simplification). Such operations introduce differences regarding the original mesh, whose evaluation is of paramount importance when choosing the processing methods to be applied for a particular purpose. Although some mesh analysis and comparison tools are described in the literature, little attention has been given to the way mesh features and mesh comparison results can be visualized. Moreover, particular functionalities have to be made available to enable systematic use and proper data analysis and exploration. PolyMeCo-a tool for polygonal mesh analysis and comparison-was designed and developed taking the above objectives into account. It enhances the way users analyze features and compare meshes by providing an integrated environment where various mesh quality measures and several visualization options are available and can be used in a coordinated way, thus leading to greater insight into the visualized data
Head-mounted display versus desktop for 3D navigation in virtual reality: A user study
No full textVirtual Reality (VR) has been constantly evolving since its early days, and is now a fundamental technology in different application areas. User evaluation is a crucial step in the design and development of VR systems that do respond to users' needs, as well as for identifying applications that indeed gain from the use of such technology. Yet, there is not much work reported concerning usability evaluation and validation of VR systems, when compared with the traditional desktop setup. The paper presents a user study performed, as a first step, for the evaluation of a low-cost VR system using a Head-Mounted Display (HMD). That system was compared to a traditional desktop setup through an experiment that assessed user performance, when carrying out navigation tasks in a game scenario for a short period. The results show that, although users were generally satisfied with the VR system, and found the HMD interaction intuitive and natural, most performed better with the desktop setup
Sectoral and regional impacts of the European carbon market in Portugal
No full textAcross Europe, CO2 emission allowances represent one of the main policy instruments to comply with the goals of the Kyoto Protocol. In this paper we use microdata to address two issues regarding the
impact of the European Carbon Market (EU ETS). First, we analyze the sectoral effects of the EU ETS in Portugal. The goal is to study the distributive consequences of imbalances, with the novelty of taking
into account firm financial data to put values into context. We show that a large majority of installations in most sectors had surpluses and the opportunity to raise remarkable revenues in some cases. We also look at the regional impact, since the pre-existing specialization of different regions in the production of different goods and services might lead to an uneven economic impact of the allowance market. In particular, Portuguese data indicate a distribution of revenue from low income to
high income regions, or rather, between installations located in those regions. We focus on the first phase of the EU ETS, using data for each one of the 244 Portuguese installations in the market as well as
financial data for 80% of these installations, although we also present data for 2008 and 2009.FCT-SFRH/BD/16726/200
A note on Gröbner bases
No full textIn this paper we introduce the new notion of co-polynomials as polynomials arising from the Graßmann–Plucker polynomials. Pairs of co-polynomials are shown to be critical in the computation of a Gröbner basis for the chirotope ideal.Centre for Research on Optimization and Control (CEOC) from the “Funda¸c˜ao para a Ciˆencia e a Tecnologia” FCT cofinanced by the European Community Fund FEDER/POCI
Transmission techniques for downlink multi-antenna MC-CDMA systems in a beyond-3G context
No full textThe combination of multiple antennas and multi-carrier code division multiple-access (MC-CDMA) is a strong candidate for the downlink of the next generation mobile communications. The study of such systems in scenarios that model real-life transmissions is an additional step towards an optimized achievement. We consider a realistic MIMO channel with two or four transmit antennas and up to two receive antennas, and channel state information (CSI) mismatches. Depending on the mobile terminal (MT) class, its number of antennas or complexity allowed, different data-rates are proposed with turbo-coding and asymptotic spectral efficiencies from 1 to 4.5 bit/s/Hz, using three algorithms developed within the European IST-MATRICE project. These algorithms can be classified according to the degree of CSI at base-station (BS): i) Transmit space-frequency prefiltering based on constrained zero-forcing algorithm with complete CSI at BS; ii) transmit beamforming based on spatial correlation matrix estimation from partial CSI at BS; iii) orthogonal space-time block coding based on Alamouti scheme without CSI at BS. All presented schemes require a reasonable complexity at MT, and are compatible with a single-antenna receiver. A choice between these algorithms is proposed in order to significantly improve the performance of MC-CDMA and to cover the different environments considered for the next generation cellular systems. For beyond-3G, we propose prefiltering for indoor and pedestrian microcell environments, beamforming for suburban macrocells including high-speed train, and space-time coding for urban conditions with moderate to high speeds. © 2005 KICS.European FP5 IST - MATRICESpanish National Project TIC2003- 09061-C03-0
Multi-user frequency pre-filtering technique for MIMO SFBC MC-CDMA systems
No full textThis paper deals with downlink space-frequency block coding (SFBC) with a multi-user pre-filtering technique for MIMO MC-CDMA systems. We consider the use of an antenna array at both the base station (BS) and the user terminal (UT). The space-frequency block codes allow that the spatial diversity be efficiently exploited and the linear multi-user frequency pre-filtering technique modulates the transmitted signal to eliminate the effects of multiple access interference (MAI) and channel distortions at the user terminals. The aim of this technique is to transfer the most computational complexity from UT to the BS, keeping the first one at very low complexity. The performance of the proposed scheme is evaluated, considering typical pedestrian scenario and both uncoded data and channel turbo coding based on UMTS specifications. © 2008 IEEE.FCT - FFT-XXI (POSI/CPS/4670/2007)PHOTON(PTDC/EEA-TEL/72890/06