Browsing by Issue Date, starting with "2006-09"
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- Joint multiuser detection and cancelation of nonlinear distortion effects for the uplink of MC-CDMA systemsPublication . Silva, Paulo; Dinis, RuiIn this paper we consider the uplink transmission in MC-CDMA systems (multicarrier coded division multiple access). To reduce the envelope fluctuations of the transmitted signals, the MC-CDMA signal associated to each MT (mobile terminal) is submitted to a clipping device, followed by a frequency-domain filtering operation. We define an iterative receiver that jointly performs the MUD (multiuser detection) and the estimation and cancellation of the nonlinear distortion effects that are inherent to the transmitted signals. Our performance results show that the proposed receiver structures allow good performances, even for severely time-dispersive channels and/or when a low-PMEPR is intended for each MT.
- An iterative detection technique for DS-CDMA signals with strong nonlinear distortion effectsPublication . Dinis, Rui; Silva, PauloWhenever a DS-CDMA signal (direct sequence code division multiple access) is the sum of several components associated to different spreading codes (e.g., the DS-CDMA signal to be transmitted by the BS (Base Station) in the downlink, or any multicode DS- CDMA signal), it has high envelope fluctuations, and a high PMEPR (Peak-to-Mean Envelope Power Ratio) setting strong linearity requirements for the power amplifiers. For this reason, it is desirable to reduce the envelope fluctuations of the transmitted signals. A promising class of nonlinear signal processing schemes, combining a nonlinear operation in the time- domain with a linear, frequency-domain filtering operation, was recently proposed for reducing the envelope fluctuations (and, inherently, the PMEPR) of DS-CDMA signals, while maintaining the spectral occupation of the corresponding conventional DS-CDMA signals. However, the performance degradation due to the nonlinear distortion effects on the transmitted signals can be relatively high, especially when a low PMEPR is intended. This can be especially serious if different powers are assigned to different spreading codes. To avoid significant performance degradation in these situations, we consider improved receiver where there is an iterative estimation and cancelation of nonlinear distortion effects. Our performance results show that the proposed receiver allows significant performance improvements after just a few iterations, even when we have strong nonlinear distortion effects.
- A spectroscopic survey of potential energy surfaces for the electronic ground state of the HO2 radical: a correction for the DMBE IV potentialPublication . Rio, CarolinaAs a result of these studies there are a variety of potentials available for performing dynamical studies on HO2, both in order to determine its rovibrational states and for modelling chemical reactions.
- Intercomparison of spectroradiometers and Sun photometers for the determination of the aerosol optical depth during the VELETA-2002 field campaignPublication . Estelles, V.; Utrillas, M. P.; Martinez-Lozano, J. A.; Alcantara, A.; Alados-Arboledas, L.; Olmo, F. J.; Lorente, J.; de Cabo, X.; Cachorro, V.; Horvath, H.; Labajo, A.; Sorribas, M.; Diaz, J. P.; Diaz, A. M.; Silva, A. M.; Elias, T.; Pujadas, M.; Rodrigues, José-António; Canada, J.; Garcia, Y.[ 1] In July 2002 the VELETA-2002 field campaign was held in Sierra Nevada ( Granada) in the south of Spain. The main objectives of this field campaign were the study of the influence of elevation and atmospheric aerosols on measured UV radiation. In the first stage of the field campaign, a common calibration and intercomparison between Licor-1800 spectroradiometers and Cimel-318 Sun photometers was performed in order to assess the quality of the measurements from the whole campaign. The intercomparison of the Licor spectroradiometers showed, for both direct and global irradiances, that when the comparisons were restricted to the visible part of the spectrum the deviations were within the instruments' nominal accuracies which allows us to rely on these instruments for measuring physical properties of aerosols at the different measurement stations. A simultaneous calibration on AOD data was performed for the Cimel-318 Sun photometers. When a common calibration and methodology was applied, the deviation was lowered to much less than 0.01 for AOD. At the same time an intercomparison has been made between the AOD values given by the spectroradiometers and the Sun photometers, with deviations obtained from 0.01 to 0.03 for the AOD in the visible range, depending on the channel. In the UVA range, the AOD uncertainty was estimated to be around 0.02 and 0.05 for Cimel and Licor respectively. In general the experimental differences were in agreement with this uncertainty estimation. In the UVB range the AOD measurements should not be used due to maximum instrumental uncertainties.
- Tierra y calPublication . Braga, Alfredo Manuel Gonçalves Silva; Robador Gonzalez, María DoloresLa construcción con tierra, al permitir despertar conocimientos an-cestrales vernaculares con tecnologías actuales, puede posibilitar una cons-trucción ecológicamente más sostenible, respetadora de los valores socio-culturales y en una dimensión verdaderamente humana. La presente comunicación presenta los primeros resultados del es-tudio experimental realizado en edificaciones del sur de Portugal que han empleado como materiales de construcción la tierra y la cal. Ensayos para obtención de la composición granulométrica, minerales arcillosos por difrac-ción de rayos X, resistencia de muestras a compresión, a flexotracción y al corte. Simulación estructural.
- Palaeosurface reconstruction based on sedimentary record and in sea level evolution in the Guadiana Estuary (Southern Iberia)Publication . Loureiro, C.; Boski, T.; Albardeiro, L.; Moura, Delminda; Terefenko, P.; Camacho, Sarita; Veiga-Pires, C.The sedimentary infilling of the Guadiana estuary, in the Southern Iberian Peninsula, has been extensively studied using a variety of laboratory methods, namely geochemical and sedimentological analyses, foraminifera assemblages and palynological profiles, supported by 14C dating [1-3](...)
- Comparative expression of mouse and chicken shisa homologues during early developmentPublication . Filipe, Mario; Gonçalves Dias da Silva, Lisa; Bento, Margaret; Silva, Ana Cristina; Belo, José A.During vertebrate embryogenesis, fibroblast growth factor (FGF) and Wnt signaling have been implicated in diverse cellular processes, including cell growth, differentiation, and tissue patterning. The recently identified Xenopus Shisa protein promotes head formation by inhibiting Wnt and FGF signaling through its interaction with the immature forms of Frizzled and FGF receptors in the endoplasmic reticulum, which prevents their posttranslational maturation. Here, we describe the mouse and chicken homologues of Xenopus Shisa. The mouse and chicken Shisa proteins share, respectively, 33.6% and 33.8% identity with the Xenopus homolog. In situ hybridization analysis shows that mouse shisa is expressed throughout embryonic development, predominantly in the anterior visceral endoderm, headfolds, somites, forebrain, optic vesicle, and limb buds. Cross-species comparison shows that the expression pattern of cshisa closely mirrors that of mshisa. Our observations indicate that the Shisa family genes are typically expressed in tissues known to require the modulation of Wnt and FGF signaling. Developmental Dynamics 235:2567-2573, 2006. (c) 2006 Wiley-Liss, Inc.
- Aljezur, um oásis no turismo algarvioPublication . Mesquita, José Carlos VilhenaO que mais impressiona em Aljezur é a pureza ambiental, e a beleza paisagística do casario que sobe até ao castelo, por entre ruelas estreitas e sinuosas, íngremes ladeiras no ardor da cal, que nos levam, no olhar atento da calçada acutilante, para as cumeadas do seu velho castelo árabe. Lá no alto, espraiando o olhar sobre o horizonte, depara-se-nos a várzea fértil, tricotada em viçosas leiras, o prateado reflexo do rio cristalino, a ebúrnea colina da Aldeia Nova, e a entrecortada linha verde da serra… Um quadro de ímpar beleza que nos faz sentir senhores do mundo, como nos tempos dos espatários conquistadores. A pureza ambiental é a pedra filosofal de Aljezur.
- Marine ornamental species from European waters: a valuable overlooked resource or a future threat for the conservation of marine ecosystems?Publication . Calado, RicardoThe worldwide growth of the marine aquarium market has contributed to the degradation of coral reef ecosystems. Enforcing the legislation on importing ornamental species has led some European traders to concentrate on local species. Portugal is used as a case study of marine ornamental fish and invertebrate collection in European waters. One hundred and seventy two species occurring in Portuguese waters (mainland, the Azores and Madeira archipelagos) were considered as potential targets for the marine aquarium industry, some of which are already traded on a regular basis (e.g. Clibanarius erythropus, Lysmata seticaudata, Cerithium vulgatum, Hinia reticulata and Ophioderma longicauda). To ensure appropriate management and conservation of these resources, the following options have been evaluated: banning the harvest and trade of all marine ornamental species from European waters; creating sanctuaries and "no take zones"; issuing collection permits; creating certified wholesalers; implementing the use of suitable gear and collecting methods; setting minimum and maximum size limits, establishing species-based quotas; protecting rare, or "key stone" species and organisms with poor survivability in captivity; establishing closed seasons; culturing ornamental organisms; and creating an "eco-fee" to support research and management. Establishing this sustainable alternative fishery may help minimise the economical and social impacts caused by the crash of important food fisheries in Portugal and other European and West African countries.
- Cirripedia of MadeiraPublication . Wirtz, Peter; Araujo, Ricardo; Southward, Alan J.We give a list of Cirripedia from Madeira Island and nearby deep water, based on specimens in the collection of the Museu Municipal do Funchal (Historia Natural) (MMF), records mentioned in the literature, and recent collections. Tesseropora atlantica Newman and Ross, 1976 is recorded from Madeira for the first time. The Megabalanus of Madeira is M. azoricus. There are 20 genera containing 27 species, of which 22 occur in depths less than 200 m. Of these shallow water species, eight are wide-ranging oceanic forms that attach to other organisms or to floating objects, leaving just 13 truly benthic shallow water barnacles. This low diversity is probably a consequence of the distance from the continental coasts and the small area of the available habitat. No endemic species have been found.