Browsing by Issue Date, starting with "2009-08"
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- Iterative detection of multicode DS-CDMA signals with strongly nonlinear transmittersPublication . Dinis, Rui; Silva, PauloWhenever a DS-CDMA signal is the sum of several components associated to different spreading codes it has high envelope fluctuations and a high peak-to-mean envelope power ratio (PMEPR) setting strong linearity requirements for the power amplifiers. The use of clipping and filtering techniques (which can be repeated several times) was shown to be an effective way of reducing the PMEPR of DS-CDMA signals. We consider an improved receiver where there is an iterative estimation and cancelation of nonlinear distortion effects. The proposed receiver allows significant performance improvements after just a few iterations, even when we have strong nonlinear distortion effects.
- 4,4 '-Di-tert-butyl-2,2 '-bipyridinePublication . Amarante, Tatiana R.; Figueiredo, Sonia; Lopes, Andre D.; Gonçalves, Isabel S.; Almeida Paz, Filipe A.In the title compound, C18H24N2, the molecular unit adopts a trans conformation around the central C-C bond [N-C-C-N torsion angle of 179.2(3)degrees], with the two aromatic rings almost coplanar [dihedral angle of only 0.70 (4)degrees]. The crystal packing is driven by co-operative contacts involving weak C H center dot center dot center dot N and C-H center dot center dot center dot pi interactions, and also the need to fill effectively the available space.
- HF spectrum occupancy and antennasPublication . Casimiro, Antonio; Azevedo, Joaquim; Economou, Lefteris; Haralambous, Haris; Tulunay, Ersin; Tulunay, Yurdanur; Bahadirlar, Yildirim; Turk, A. Serdar; Warrington, E. MichaelThis paper deals with the research made during the COST 296 action in the WG2, WP 2.3 in the antennas and HF spectrum management fields, focusing the Mitigation of Ionospheric Effects on Radio Systems as the subject of this COST action.
- Effects of endolithic parasitism on invasive and indigenous mussels in a Variable Physical EnvironmentPublication . I Zardi, Gerardo; Nicastro, Katy; McQuaid, Christopher David; Gektidis, MarcosBiotic stress may operate in concert with physical environmental conditions to limit or facilitate invasion processes while altering competitive interactions between invaders and native species. Here, we examine how endolithic parasitism of an invasive and an indigenous mussel species acts in synergy with abiotic conditions of the habitat. Our results show that the invasive Mytilus galloprovincialis is more infested than the native Perna perna and this difference is probably due to the greater thickness of the protective outer-layer of the shell of the indigenous species. Higher abrasion due to waves on the open coast could account for dissimilarities in degree of infestation between bays and the more wave-exposed open coast. Also micro-scale variations of light affected the level of endolithic parasitism, which was more intense at non-shaded sites. The higher levels of endolithic parasitism in Mytilus mirrored greater mortality rates attributed to parasitism in this species. Condition index, attachment strength and shell strength of both species were negatively affected by the parasites suggesting an energy trade-off between the need to repair the damaged shell and the other physiological parameters. We suggest that, because it has a lower attachment strength and a thinner shell, the invasiveness of M. galloprovincialis will be limited at sun and wave exposed locations where endolithic activity, shell scouring and risk of dislodgement are high. These results underline the crucial role of physical environment in regulating biotic stress, and how these physical-biological interactions may explain site-to-site variability of competitive balances between invasive and indigenous species.
- Turbo equalization with cancelation of nonlinear distortion for CP-assisted and zero-padded MC-CDM schemesPublication . Dinis, Rui; Silva, Paulo; Araújo, TeresaIn this paper, we consider MC-CDM schemes (MultiCarrier Code Division Multiplexing) where clipping techniques are employed to reduce the envelope fluctuations of the transmitted signals. Both CP-assisted (Cyclic Prefix) and ZP (Zero- Padded) MC-CDM schemes are studied. We develop frequencydomain turbo equalizers combined with an iterative estimation and cancelation of nonlinear distortion effects, with relatively low complexity since they allow FFT-based (Fast Fourier Transform), frequency-domain implementations. Our performance results show that the proposed receivers allow significant performance improvements at low and moderate SNR (Signal-to-Noise Ratio), even when strongly nonlinear transmitters are employed. The receiver for ZP MC-CDM is of special interest for systems where the duration of the channel impulse response is not a small fraction of the duration of the MC-CDM blocks, being suitable to MC-CDM systems with very large blocks (hundreds or even thousands of subcarriers), since they do not require the inversion nor the multiplication of large matrixes.
- Mechanisms of left-right asymmetric signal generation around the nodePublication . Kawasumi, Aiko; Iwai, Naomi; Belo, José A.; Nakamura, Tetsuya; Shiratori, Hidetaka; Hamada, Hiroshi
- Como se faz uma recensão críticaPublication . Mesquita, José Carlos VilhenaUma recensão crítica é uma avaliação e como tal deve ser operada com rigor e isenção, unicamente por especialistas na matéria cuja apreciação deve ser chancelada por uma instituição científica, para que a mesma possa ter credibilidade e ser objecto de referência. O recensor (passo o neologismo) é um ser crítico, que deve pugnar pelo progresso da ciência e do conhecimento, através do seu distanciamento da obra e do autor, fazendo da isenção e da objectividade a sua bandeira e o seu lema de trabalho. Basta estes dois atributos para que a sua recensão possa ser credível e respeitada.
- Adaptation to reduced salinity affects the olfactory sensitivity of Senegalese sole (Solea senegalensis Kaup 1858) to Ca2+ and Na+ but not amino acidsPublication . Velez, Zélia; Hubbard, Peter; Barata, E. N.; Canario, Adelino V. M.The Senegalese sole is a marine flatfish, which often penetrates into estuarine waters to feed. It cannot, however, survive in full freshwater. The current study investigated the effect of adaptation to low salinity (10‰) on olfactory responses to changes in environmental [Ca2+] and [Na+] and amino acids by the electro-encephalogram (EEG) recorded from the olfactory bulb. The sole showed olfactory responses to increases in environmental [Na+] and decreases in environmental [Ca2+]; sensitivity to Na+ was greater at 10‰ whereas sensitivity to Ca2+ was greater at 35‰. Decreased environmental [Na+] increased sensitivity to changes in [Ca2+] whereas increased environmental [Ca2+] decreased bulbar responses to changes in [Na+]. Sensitivity to amino acids was unaffected by external salinity. However, the absence of external Na+ strongly decreased bulbar responses to amino acids in fish adapted to 35‰ seawater but not in those at 10‰. The absence of external Ca2+ had no such effect at either salinity. This suggests that odorant-receptor binding and/or olfactory transduction is reliant on external Na+ (but not Ca2+) at higher salinities but the olfactory system is able to adapt to lower environmental [Na+]. Taken together, these results suggest that reductions of external salinity modulate olfactory sensitivity to environmental Ca2+ and Na+ but not amino acids. However, at low salinities, olfactory sensitivity to amino acids is maintained by decreasing reliance on external Na+.
- A Minha Rua, de Ernesto SilvaPublication . Mesquita, José Carlos VilhenaA poesia é uma das formas mais elevadas de propugnar pelos sublimes ideais da liberdade, da igualdade, da solidariedade, da paz, da fraternidade e do amor. São esses valores que aqui vemos estampados na obra de Ernesto Silva. De uma forma simples mas elevada, sem falsas erudições nem balofos pretensiosismos intelectuais, o autor construiu ao longo de quarenta e cinco anos uma verdadeira girândola poética, versando as mais diversificadas temáticas em singelos poemas de um inebriante perfume naturalista e duma esfuziante musicalidade popular.
- Neogastropod phylogenetic relationships based on entire mitochondrial genomesPublication . Cunha, R. L.; Grande, Cristina; Zardoya, R.The Neogastropoda is a highly diversified group of predatory marine snails (Gastropoda: Caenogastropoda). Traditionally, its monophyly has been widely accepted based on several morphological synapomorphies mostly related with the digestive system. However, recent molecular phylogenetic studies challenged the monophyly of Neogastropoda due to the inclusion of representatives of other caenogastropod lineages (e.g. Littorinimorpha) within the group. Neogastropoda has been classified into up to six superfamilies including Buccinoidea, Muricoidea, Olivoidea, Pseudolivoidea, Conoidea, and Cancellarioidea. Phylogenetic relationships among neogastropod superfamilies remain unresolved. Results The complete mitochondrial (mt) genomes of seven Neogastropoda (Bolinus brandaris, Cancellaria cancellata, Conus borgesi, Cymbium olla, Fusiturris similis, Nassarius reticulatus, and Terebra dimidiata) and of the tonnoidean Cymatium parthenopeum (Littorinimorpha), a putative sister group to Neogastropoda, were sequenced. In addition, the partial sequence of the mitochondrial genome of the calyptraeoidean Calyptraea chinensis (Littorinimorpha) was also determined. All sequenced neogastropod mt genomes shared a highly conserved gene order with only two instances of tRNA gene translocation. Phylogenetic relationships of Neogastropoda were inferred based on the 13 mt protein coding genes (both at the amino acid and nucleotide level) of all available caenogastropod mitochondrial genomes. Maximum likelihood (ML) and Bayesian inference (BI) phylogenetic analyses failed to recover the monophyly of Neogastropoda due to the inclusion of the tonnoidean Cymatium parthenopeum within the group. At the superfamily level, all phylogenetic analyses questioned the taxonomic validity of Muricoidea, whereas the monophyly of Conoidea was supported by most phylogenetic analyses, albeit weakly. All analyzed families were recovered as monophyletic except Turridae due to the inclusion of Terebridae. Further phylogenetic analyses based on either a four mt gene data set including two additional Littorinimorpha or combining mt and nuclear sequence data also rejected the monophyly of Neogastropoda but rendered rather unresolved topologies. The phylogenetic performance of each mt gene was evaluated under ML. The total number of resolved internal branches of the reference (whole-mt genome) topology was not recovered in any of the individual gene phylogenetic analysis. The cox2 gene recovered the highest number of congruent internal branches with the reference topology, whereas the combined tRNA genes, cox1, and atp8 showed the lowest phylogenetic performance. Conclusion Phylogenetic analyses based on complete mt genome data resolved a higher number of internal branches of the caenogastropod tree than individual mt genes. All performed phylogenetic analyses agreed in rejecting the monophyly of the Neogastropoda due to the inclusion of Littorinimorpha lineages within the group. This result challenges morphological evidence, and prompts for further re-evaluation of neogastropod morphological synapomorphies. The important increase in number of analyzed positions with respect to previous studies was not enough to achieve conclusive results regarding phylogenetic relationships within Neogastropoda. In this regard, sequencing of complete mtDNAs from all closely related caenogastropod lineages is needed. Nevertheless, the rapid radiation at the origin of Neogastropoda may not allow full resolution of this phylogeny based only on mt data, and in parallel more nuclear sequence data will also need to be incorporated into the phylogenetic analyses.