Browsing by Author "Correia, Victor"
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- Chronology of the sedimentary processes during the postglacial sea level rise in two estuaries of the Algarve coast, Southern PortugalPublication . Boski, T.; Camacho, Sarita; Moura, Delminda; Fletcher, William; Wilamowski, A.; Veiga-Pires, C.; Correia, Victor; Loureiro, C.; Santana, PauloFour profiles of estuarine sediments obtained from boreholes drilled in the Algarve, Southern Portugal were studied in order to reconstruct the process of sediment accumulation driven by the postglacial sea level rise. In addition to the sedimentological analysis, the Foraminifera Index of Marine Influence (FIMI) permitted assessment of the nature and organization of sedimentary facies in the BelicheeGuadiana and Gilão-Almargem estuaries. The Beliche- Guadiana CM5 and Almargem G2 profiles accumulated in a sheltered environment, with the former presenting an almost continuous record of the sea level rise since ca 13 000 cal yr BP. The G1 and G3 profiles from the Gilão-Almargem area represent a more discontinuous record of the last 8000 years, which accumulated in the more dynamic environment of an outer estuary. The integration of all radiocarbon ages of dated levels, led to an estimate of sediment accumulation rates. Assuming a constant position of the sediment surface with respect to the tidal range and a negligible compaction of sediment, the sea level rose at the rate of 7 mm yr ^-1 in the period from 13 000 to 7500 cal yr BP. This process slowed down to ca 0.9 mm yr 1 from 7500 cal yr BP until the present. The marked historical change in the rate of sediment accumulation in these estuaries also occurred with the accumulation of organic matter and is, therefore, important data for global biogeochemical models of carbon. The main obstacle to obtain higher temporal resolution of the sedimentary processes was the intense anaerobic respiration of organic matter via sulphate reduction, which did not allow any accumulation of peat and, furthermore, led to erasure of the palaeontological record by acid formed from the subsequent oxidation of sulphides.
- Core and patch position optimizations for vibration control of piezolaminated structuresPublication . Moita, José Mateus Simões; Correia, Victor; Soares, Cristovão M. Mota; Soares, Carlos A. MotaThis paper deals with a finite formulation baserd on the classical laminated plate tehory, for active control of thin late laminated structures with integrated piezoelectric layers, acting as sensors and actuators. The control is initialized through a previuos optimization of the core of the laminated structure, in order to minimize the vibration amplitude. Also the optimization of the patches position in performed to maximize the piezoelectric actuator efficiency. the simulating annealing mthod is used for these purposes. The finite element model is a single layer triangular nonconforming plate/shell element with 18 degrees of fredom for the generalized displacements, and one electrical potential degree of freedom for each piezoelectric element layer, wich can be surface bonded or imbedded on the laminate. To achieve a mechanism of active control of the structure dynamic response, a feedback control algorirhm is used, coupling the sensor and active piezoelectric layers. To calculate the dynamic response of the laminated structures the Newmark method is considered. The model is applied in the solution of an illustrative case and the results are presented and discussed.
- Diagenese, fluxo sedimentar e subida global do nível do mar como factores de controle da geoquímica dos sedimentos estuarinosPublication . Boski, T.; Wilamowski, A.; Moura, Delminda; Correia, Victor; Veiga-Pires, C.; Santana, Paulo0 presente texto apresenta a discussão dos mais recentes resultados de estudo da geoquímica e mineralogia das sequências sedimentares acumuladas durante Plistocénico terminal e Holocénico nos dois principais estuários da Costa Sul Portuguesa, Estuário do Rio Guadiana e Estuário do Rio Arade. Em ambos, verifica-se um processo de rápida acumulação de massa sedimentar ate ca 7000 anos cal BP, sob a influência de rápida subida pós-glacial do mmm. A partir desta altura ate o presente a sedimentação nos sistemas estuarinos passa a ser sobretudo controlada pela redistribuição dos sedimentos localmente disponíveis. No estuário do Arade a proximidade entre a área alimentadora e a área de deposição reflecte-se pela abundância c diversidade dos minerais pesados erodidos do Maciço Alcalino de Monchique e da faixa vulcânica . No Estuário do Guadiana a assinatura da bacia de drenagem e menus espectacular dada a monotonia mineralógica do Flish Varisco. A sulfatoredução. oxidação dos sulfuretos e neoformação dos carbonatos são os principais processos de diagenése mineral, ligada a ciclo da matéria orgânica (MO) acumulada nos sedimentos. A taxa media de acumulação da MO que até 7000 a a calBP é aproximadamente 200 g m-2/ano-1 diminui posteriormente até aproximadamente 30% desse valor.
- Does the glacial/interglacial sea-level changes modulate the atmospheric CO2 variations?Publication . Boski, T.; Moura, Delminda; Veiga-Pires, C.; Fletcher, William; Correia, VictorIt is postulated the rate of the terrestrial organic carbon (OC) retention around the moving ocean/continent interface is strongly affected by the sea-level.
- Postglacial organic carbon accumulation in coastal zones-A possible cause for varying atmospheric CO2 levels: preliminary data from SW PortugalPublication . Boski, T.; Moura, Delminda; Correia, Victor; Martins, H.; Veiga-Pires, C.; Camacho, Sarita; Wilamowski, A.We report the preliminary data on organic carbon accumulation rates which are being determined in the infill sequences of several estuaries, in the coastal fringe of Algarve (S Portugal). The so far analysed sedimentary sequences of Guadiana River estuary represent the time span from ca 10000 yr. cal BP to present. The obtained data indicate that until ca 7000 yr. cal BP, i.e. during the period of fast sea level rise, organic carbon accumulated at an average rate ranging from 160 to 320 gm yr . In the Middle and Upper Holocene, when the sea level rise was not exceeding 25cm/century the organic carbon accumulation rate dropped to an average value of ca 50 gm yr . The analysis of gas bubble content from ice cores indicates that the atmospheric CO concentration evolved during the last glacial/interglacial transition, from 180 ppv minimum during the LGM to the 270 ppmV preindustrial level. Considering that the terrestrial particulate organic matter is an essential fertiliser of the ocean, it is postulated that enhanced burial of POM in the coastal areas during the period of fast postglacial sea level rise is responsible for decrease of primary productivity in the open ocean and consequent transfer of 200 Gt. ofCto the atmosphere.