Browsing by Author "Pereira, L."
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- Comparing the performance of the SF-6D and EQ-5D across diseasesPublication . Ferreira, L.; Ferreira, P.; Pereira, L.
- Diastolic dysfunction in liver cirrhosis: prognostic predictor in liver transplantation?Publication . Carvalheiro, F.; Rodrigues, C.; Adrego, T.; Viana, J.; Vieira, H.; Seco, C.; Pereira, L.; Pinto, F.; Eufrásio, Ana; Bento, C.; Furtado, E.Background. Patients with liver cirrhosis may develop cirrhotic cardiomyopathy (CC), characterized by blunted contractile responsiveness to stress, diastolic dysfunction (DD), and electrophysiological abnormalities. It may adversely affect the long-term prognosis of these patients.Methods. We conducted a retrospective analysis of patients undergoing liver transplantation (LT) for cirrhosis from January 2012 to June 2015. We analyzed demographic characteristics, the etiology of cirrhosis, Child-Pugh and Model for End-Stage Liver Disease (MELD) scores, the corrected QT (QTc) interval in the preoperative period, diastolic and systolic dysfunction, mortality and survival, and duration of mechanical ventilation and vasopressor support in the post-LT period. These variables were compared with diastolic dysfunction and prolongation of QTc, with the use of chi-square, Fisher, and Mann-Whitney U tests.Results. The study included 106 patients, 80.2% male and overall average age 54.83 years. The median MELD score was 16, and Child-Pugh class C in 55.4%. Prolonged QTc interval before LT was present in 19% and DD in 35.8% of patients. QTc before LT or DD did not vary significantly with MELD or Child-Pugh score.Conclusions. The patients in the pre-LT period presented with a significant incidence of DD, which can predispose them to adverse cardiac events. The presence of DD correlates with mortality after LT in patients with hepatic cirrhosis.
- Electrical AC behaviour of MPCVD diamond Schottky diodesPublication . Pereira, L.; Rodrigues, A.; Gomes, Henrique L.; Pereira, E.The present work reports some experimental results on the electrical AC behaviour of metal-undoped diamond Schottky diodes fabricated with a free-standing MPCVD diamond film (5 mum thick). The metals are gold for the ohmic contact and aluminium for the rectifier. The capacitance and loss tangent vs, frequency shows that capacitance presents a relaxation maximum at frequencies near 10 kHz at room temperature. Although the simple model (small equivalent circuit) can justify the values for the relaxation, it cannot justify the departure from the Debye model, also verified in the Cole-Cole plot. Taking into account the existence of traps in the depletion region, a best fit to the experimental results was obtained. The difference between the Fermi level and the band edge of 0.2-0.3 eV is in agreement with the activation energy found from the loss tangent analysis. The capacitance with applied voltage (Mott-Schottky plots) gives a defect density of 10(16) cm(-3) with contact potentials near 0.5 V and the profile of defect density obtained shows a major density (approx. 10(17) cm(-3)) in a layer with a thickness less than 50 nm from the junction, decreasing by one order of magnitude with increasing distance. Finally a structural model is proposed to explain the AC behaviour found. (C) 2001 Elsevier Science B.V. All rights reserved.
- Electrical characterization of CVD diamond-n(+) silicon junctionsPublication . Rodrigues, A. M.; Gomes, Henrique L.; Stallinga, Peter; Pereira, L.; Pereira, E.The electrical characteristics of CVD-diamond/n(+)-Si heterojunction devices are reported. Below 250 K the diodes show an unusual inversion of their rectification properties. This behavior is attributed to an enhanced tunneling component due to interface states, which change their occupation with the applied bias. The temperature dependence of the loss tangent shows two relaxation processes with different activation energies. These processes are likely related with two parallel charge transport mechanisms, one through the diamond grain, and the other through the grain boundary. (C) 2001 Elsevier Science B.V. Ah rights reserved.
- Interface properties and capacitance-voltage behaviour of diamond devices prepared by microwave-assisted CVDPublication . Rodrigues, A. M.; Gomes, Henrique L.; Rees, J. A.; Pereira, L.; Pereira, E.Free standing diamond films were used to study the effect of diamond surface morphology and microstructure on the electrical properties of Schottky barrier diodes. By using free standing films both the rough top diamond surface and the very smooth bottom surface are available for post-metal deposition. Rectifying electrical contacts were then established either with the smooth or the rough surface. The estimate of doping density from the capacitance-voltage plots shows that the smooth surface has a lower doping density when compared with the top layers of the same film. The results also show that surface roughness does not contribute significantly to the frequency dispersion of the small signal capacitance. The electrical properties of an abrupt asymmetric n(+)(silicon)-p(diamond) junction have also been measured. The I-V curves exhibit at low temperatures a plateau near zero bias, and show inversion of rectification. Capacitance-voltage characteristics show a capacitance minimum with forward bias, which is dependent on the environment conditions. It is proposed that this anomalous effect arises from high level injection of minority carriers into the bulk.
- Uma janela educativa para o oceano Jurássico - o Planalto do EscarpãoPublication . Oliveira, Sónia; Veiga-Pires, C.; Moura, Delminda; Pereira, L.Situado na região mais a sudoeste da Europa, o aspirante a Geoparque Mundial da Unesco Algarvensis (aUGGp Algarvensis) é um território identitário e inspirador que visa contribuir para uma maior coesão social e territorial dos concelhos de Loulé, Silves e Albufeira, através de uma política de valorização do território, baseada no conceito de Geoparque UNESCO, com o apoio da Universidade do Algarve. O aUGGp Algarvensis possui um património geológico de relevo internacional e nacional sobre uma área territorial com cerca de 1381 km2 , e pertencente a três concelhos do Algarve central. O Projeto coliderado pela Universidade do Algarve e o Centro de Investigação Marinha e Ambiental (CIMA|Arnet-Ualg) alia uma estratégia de geoconservação e um conjunto de políticas de educação e sensibilização ambiental, à promoção de um desenvolvimento socioeconómico sustentável baseado em atividades de geoturismo, envolvendo as comunidades locais e contribuindo para a valorização e promoção dos produtos locais. Esta estratégia de desenvolvimento sustentável conjugada à geologia da região permitiu definir os limites do aUGGp Algarvensis, formando um território coeso que não se estende até ao mar e que tem 48,8 % da sua área constituída por freguesias consideradas com baixa densidade populacional. O seu território e as suas paisagens cromáticas são os testemunhos de uma história geológica que conta o nascimento e aplanamento de cadeias montanhosas (Pérmico e Triásico) e mares antigos (Carbonífero e Jurássico), e se estende desde muito antes dos continentes terem a sua configuração atual, ou mesmo dos dinossauros existirem, até aos dias de hoje (Quaternário). As paisagens superficiais e subterrâneas do território do aUGGp Algarvensis escondem uma grande geodiversidade de geossítios, cujo levantamento e inventariação ainda se encontram em curso.
- Microelectrical characterisation of diamond films: an attempt to understand the structural influence on electrical transport phenomenaPublication . Pereira, L.; Pereira, E.; Gomes, Henrique L.; Rodrigues, A.; Rees, A.; Cremades, A.; Piqueras, J.The properties of microelectrical conduction in microwave plasma assisted chemical vapour deposition (MPCVD) diamond films were investigated using an atomic force microscopy probe, giving a morphological map of the electrical conduction with a spatial resolution better than 500 nm. Also, a cathodoluminescence map with a spatial resolution of about 1 mu m was obtained, giving the possibility of correlating the defects involved in the different carrier transport phenomena. Using micro-Raman analysis several bands could be identified. It is found that the defects responsible for the cathodoluminescence (CL) blue band are responsible for the major part of the electrical conduction in diamond films, while the defects localised in < 111 > surfaces, responsible for the green CL emission, could be involved in a less conductive process. (C) 2000 Elsevier Science S.A. All rights reserved.
- Photoconductivity and electrical properties of diamond films grown by MPCVDPublication . Pereira, L.; Pereira, E.; Gomes, Henrique L.The electrical and photoconductive features of as-grown microwave-plasma-assisted chemical-vapour deposition (MPCVD) diamond films are studied in correlation with magnetic results obtained from electron paramagnetic resonance (EPR). Also, the morphology is analysed by atomic force microscopy (AFM) showing [111] crystals with a good uniformity of the deposit. The photoresponse as well the current-voltage features observed show an efficient photogeneration of carriers while the optoelectronic characteristics of the metal-diamond junction have an ideality factor of 1.6 together with a rectification ratio of about 10(4) at +/-2.5 V. The nature of the mechanisms responsible for the conduction is discussed. (C) 1998 Elsevier Science S.A.
- Polycrystalline diamond thin film as wide bandgap material: the optoelectronic behaviour and the relationship with the structurePublication . Pereira, L.; Pereira, E.; Rodrigues, A. M.; Gomes, Henrique L.In this work metal - Microwave Plasma CVD diamond Schottky devices were studied. The current density vs. applied voltage reveals rectification ratios up to 10(4) at \ +/- 2V \. Under illumination an inversion and increase of the rectification is observed. The carrier density is 10(15) cm(-3) and the ideality factors near 1.5. The dark current vs. temperature shows that below 150 K the bulk transport is controlled by a hopping process with a density of defects of 10(16) cm(-3). For higher temperatures an extrinsic ionisation with activation energy of 0.3 eV takes place. The correlation with the polycrystalline nature of the samples is focused.
- Sea-level rise and anthropogenic activities recorded in the late Pleistocene/Holocene sedimentary infill of the Guadiana Estuary (SW Iberia)Publication . Delgado, J.; Boski, T.; Nieto, J. M.; Pereira, L.; Moura, Delminda; Gomes, A.I.; Mendes da Silva de Sousa, Carlos A; García-Tenorio, R.This study reviews data on sea-level rise during the last 13000 yr cal. BP (13 kyr) as recorded in the estuarine sediments of the Guadiana River (SE Portugal, SW Spain). We combined new data from a 63 m-long borehole, drilled through the entire postglacial sedimentary sequence, with information on five previously studied cores. By integrating sedimentological, geochemical and palaeontological proxies, we were able to make a palaeoenvironmental reconstruction of the Guadiana terminal palaeovalley during the last 13 kyr and propose a curve of sea-level rise for the SW Iberian Atlantic margin. Our foraminifera-based palaeoecological reconstruction, anchored to a 14C age model, reveals rapid sea-level rise from 13 kyr, interrupted during the Younger Dryas and resuming ca 11.5 kyr. The pace of marine transgression slackened ca. 7.5 kyr and since then has progressed upwards at a rate of 1.2 mm yr 1. HoloceneeAnthropocene sediments from two boreholes were also analysed to assess the timing, levels and sources of trace metals produced by acid mine drainage from the Iberian Pyrite Belt. Study of metal/aluminium ratios through the profiles allowed background metal concentrations to be estimated from lithostratigraphic units older than ca. 5 kyr (i.e. unaffected by anthropogenic activities). Human activities are especially evident from 4.5 kyr (the beginning of the Copper Age), with anthropogenic sources of metal fluxes prevailing over natural sources (especially Pb, Co, Ni, and Mn, and, to a lesser extent, Zn, Cu, and Ni). Mining activities became particularly intensive between the late Bronze Age and the Roman period (3e1.5 kyr), when the highest metal enrichment factors were recorded: EFPb z 2, EFCd > 10, EFCr z 2, EFCu z 3, EFZn ¼ 1.4.This study reveals the utility of postglacial sedimentary records for reconstructing historical changes in regional water-sediment quality and separating natural and anthropogenic sources of geochemical contaminants.