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Influence of the stimulated raman scattering on the four-wave mixing process in birefringent fibers
No full textThe influence of the stimulated Raman scattering in the four-wave mixing process in high birefringent fibers is theoretically analyzed. We consider the dual pump configuration in both co-polarized and orthogonal polarization schemes and treat simultaneously the stimulated Raman scattering and the four-wave mixing processes. The obtained results are valid even when the shift between the pumps and signal lies inside the Raman band. Results show that when the phase-matching condition is achieved the generation of the idler wave is mostly dependent on the real part of the fiber nonlinear response function, whereas the amplification of the signal wave is mostly dependent on the imaginary part. Results also show that when the phase-matching condition is satisfied the optical power evolution of the signal and idler waves for small frequency detunings are mostly described by the anisotropic Raman response of the fiber, whereas for high frequency detunings the isotropic response dominates. Our analysis also shows that the stimulated Raman scattering can increase the efficiency of the four-wave mixing process, for certain frequency detunings
Low-cost Raman amplifier for CWDM systems
No full textWe propose a low-cost Raman based amplification scheme for coarse wavelength division multiplexing systems. We also present a mathematical model suitable to be used in the design, analyze and optimization of Raman amplification systems. We validate the mathematical model with extensive comparisons with experimental results. Good agreement is obtained between numerical and experimental results. An amplification system offering more than 18 dB of gain over more than 80 nm is obtained using only four low power (up to 500 mW) semiconductor lasers. (c) 2007 Wiley Periodicals, Inc
Estudos de difusão em polímeros utilizando sensores de ondas acústicas
No full textMestrado em Métodos Instrumentais e Controlo de Qualidade AnalíticaAs embalagens alimentares desempenham um papel essencial na garantia da
qualidade dos alimentos durante o seu tempo de vida útil. Graças ao crescente
desenvolvimento tecnológico, a produção destas embalagens tem evoluído no
sentido de se adaptar às necessidades, cada vez mais exigentes, da
preservação dos alimentos, sendo o plástico o principal material usado nas
embalagens alimentares. Para que a protecção seja eficaz é necessário
garantir que os agentes externos não entram em contacto com os alimentos
de forma a alterar a sua qualidade. A caracterização destes plásticos quanto
às suas propriedades de barreira a vapores e gases do meio exterior é
fundamental para melhorar a preservação dos alimentos.
Este trabalho tem como objectivo desenvolver um novo método analítico para
fazer estudos de difusão de gases através de filmes poliméricos usados nas
embalagens alimentares. A utilização da Microbalança de Cristais de Quartzo
adaptada a uma Célula de Permeação especialmente concebida para este
projecto, veio permitir medições da permeação em tempo real. Esta técnica
apresenta uma elevada sensibilidade, é experimentalmente simples e
económica, revelando-se adequada para estudar a difusão de compostos
voláteis como aminas, em filmes aderentes de PET, PVC e LDPE.Food packaging constitutes an essential tool for preserving food products
quality throughout its life cycle. Thanks to a growing technological
development, the manufacturing of these packaging has evolved towards the
fulfilment of the needs and demands, of food preservation. In that context,
plastic is the main raw material used in food packaging. For the effectiveness
of the protection, it is necessary to avoid contact between external agents and
food products in order to maintain quality. The characterization of plastics
concerning their barrier properties to external vapours and gases is
fundamental to improve food preservation.
The objective of this work is the development of a new analytical method to
study gases diffusion through polymeric films used in food packaging. The use
of a Quartz Crystal Microbalance converted to a permeation cell specially
developed for this project makes possible the acquisition of permeation data in
real time. This technique is highly sensitive, inexpensive and simple to use and
showed to be adequate to study the diffusion of volatile compounds, like
amines, through adherent films of PET, PVC and LDPE
Explicit representation of the green's function for the three-dimensional exterior Helmholtz equation
No full textWe construct a sequence of solutions of the exterior Helmholtz equation such that their restrictions form
an orthonormal basis on a given surface. The dependence of the coefficients of these functions on the
coefficients of the surface are given by an explicit algebraic formula. In the same way, we construct an
explicit normal derivative of the Dirichlet Green’s function. We also construct the Dirichlet-to-Neumann
operator. We prove that the normalized coefficients are uniformly bounded from zero.PTDC/MAT/72840/2006CEOCFCTFEDER/ POCT
Ultrastructure and LSU rDNA-based revision of Peridinium group Palatinum (Dinophyceae) with the description of Palatinus gen. nov.
No full textThe name Peridinium palatinum Lauterborn currently designates a freshwater peridinioid with 13 epithecal and six cingular plates, and no apical pore complex. Freshwater dinoflagellate floras classify it in Peridinium group palatinum together with P. pseudolaeve M. Lefevre. General ultrastructure, flagellar apparatus, and pusular components of P. palatinum were examined by serial section TEM and compared to P. cinctum (O. F. Mull.) Ehrenb. and Peridiniopsis borgei Lemmerm., respectively, types of Peridinium and Peridiniopsis. Partial LSU rDNA sequences from P. palatinum, P. pseudolaeve and several peridinioids, woloszynskioids, gymnodinioids, and other dinoflagellates were used for a phylogenetic analysis. General morphology and tabulation of taxa in group palatinum were characterized by SEM. Differences in plate numbers, affecting both the epitheca and the cingulum, combine with differences in plate ornamentation and a suite of internal cell features to suggest a generic-level distinction between Peridinium group palatinum and typical Peridinium. The branching pattern of the phylogenetic tree is compatible with this conclusion, although with low support from bootstrap values and posterior probabilities, as are sequence divergences estimated between species in group palatinum, and typical Peridinium and Peridiniopsis. Palatinus nov. gen. is proposed with the new combinations Palatinus apiculatus nov. comb. (type species; syn. Peridinium palatinum), P. apiculatus var. laevis nov. comb., and P. pseudolaevis nov. comb. Distinctive characters for Palatinus include a smooth or slightly granulate, but not areolate, plate surface, a large central pyrenoid penetrated by cytoplasmic channels and radiating into chloroplast lobes, and the presence of a peduncle-homologous microtubular strand. Palatinus cells exit the theca through the antapical-postcingular area.FCT-POCI/SFRH/BD/16794/2004SYNTHESYS project DK-TAF 4706Villum-Kann Rasmussen Foundatio
Architecture of the flagellar apparatus and related structures in the type species of Peridinium, P-cinctum (Dinophyceae)
No full textThe ultrastructure of Peridinium cinctum, was examined by serial sectioning with particular emphasis on the detailed construction of the flagellar apparatus. The pusular system of P. cinctum included two sac pusules in open connection with the flagellar canals; disorganized material was found inside the pusules and near the flagellar pores, indicating excretory activity of the pusules. Several cells had replicated basal bodies, which were oriented toward the cell apex. The functional basal bodies formed an angle of about 65 degrees and were linked by a layered connective, a structure so far seen only in peridinioids. A transverse microtubular root looped around the transverse flagellar canal and nucleated several rows of microtubular extensions that lined most of the transverse sac pusule. A single-stranded root was associated with the surface of the longitudinal basal body almost at a right angle to the basal body triplets. A fibrous connective between the transverse striated root and the longitudinal microtubular root was absent. The striated collars encircling the flagellar pores had a complex structure and were linked by a large connective; a smaller fibrous connective was also found in one cell. An extension of the longitudinal striated collar lined part of the longitudinal sac pusule; it showed a tubular substructure and was perhaps contractile. Bacteria were present in the peripheral cytoplasm of the cell, enveloped by several unit membranes and surrounded by vacuoles; near the sac pusules they appeared disorganized with aggregated ribosomes, possibly the result of digestion.JNICT-PRAXIS XXI/BD/3887/9
Taxonomy and ultrastructure of a freshwater, heterotrophic Amphidinium (Dinophyceae) that feeds on unicellular protists
No full textAmphidinium lacustre Stein, non sensu auctt, was identified by reference to original descriptions, which differ significantly from later interpretations. Mixed cultures containing A. lacustre, cryptomonads, Spermatozopsis exsultans Korshikov, and small chlorelloid cells were examined for feeding events. The dinoflagellate ingested the cytoplasm of cryptomonads, leaving the periplast, and completely ingested Spermatozopsis and chlorelloid cells. A peduncle was used in the initial stages of prey capture, although it was not visible during food uptake. The ultrastructure of A, lacustre was typical of unarmored dinoflagellates. A single pusule per cell, consisting of one long; convoluted tube, opened directly into one of the flagellar canals. An eyespot was present, composed of presumably crystalline, vesicle-contained units, similar to those of Gymnodinium natalense Horiguchi et Pienaar. The main components of the flagellar apparatus resembled those of other Amphidinium species, but differences were noted. The transverse basal body overlapped the proximal end of the longitudinal one at an angle of about 120 degrees Three connectives were distinguished between basal bodies, one of which consisted of radiating fibers linking individual triplets of the longitudinal basal body to one triplet of the transverse. Some flagellar apparatus components were closely associated to a vesicle and to a mitochondrion. A ventral ridge extended from the (incomplete) longitudinal striated collar to the peduncular striated collar. The peduncle was supported by a single strand of microtubules, which were surrounded by numerous vesicles with electron-opaque contents.JNICT-PRAXIS XXI/BD/3887/9
Multiple positive solutions for a p-Laplacian dirichlet problem with superdiffusive reaction
No full textResumo não disponível..
On a p-Superlinear Neumann p-Laplacian equation
No full textWe consider a nonlinear Neumann problem, driven by the p-
Laplacian, and with a nonlinearity which exhibits a p-superlinear growth
near infinity, but does not necessarily satisfy the Ambrosetti–Rabinowitz
condition. Using variational methods based on critical point theory, together
with suitable truncation techniques and Morse theory, we show that
the problem has at least three nontrivial solutions, of which two have a fixed
sign (one positive and the other negative)
Surrender or resistance to the implementation of Local Agenda 21 in Portugal: the challenges of local governance for sustainable development
No full textThe aim of this paper is to understand how Local Agenda 21 (LA21) is
contributing to update local policy and decision making towards sustainable
development in Portugal. Departing from a theoretical view of governance for
sustainable development – its core values and challenges – and the role of LA21 in
its endorsement, the paper presents the main results of a questionnaire survey
submitted to Portuguese municipalities, with the purpose of understanding how
far LA21 is being incorporated into planning and management. The paper then
tries to expose some of the main potential, limitations and challenges in the local
Portuguese case for the short-term sustainable future