Experimental study of proton induced nuclear reactions in 6,7 Li

This work presents the results of the experimental study of proton induced nuclear reactions in lithium, namely the 7Li(p,α) 4He, 6Li(p,α) 3He and 7Li(p,p)7Li reactions. The amount of 7Li and 6Li identified as primordial and observed in very old stars of the Milky Way galactic halo strongly deviates from the predictions of primordial nucleosynthesis and stellar evolution models which depend, among other factors, on the cross sections of reactions like 7Li(p,α) 4He and 6Li(p,α) 3He. These discrepancies have triggered a large amount of research in the fields of stellar evolution, cosmology, pre-galactic evolution and low energy nuclear reactions. Focusing on nuclear reactions, this work has measured the 7Li(p,α) 4He and 6Li(p,α) 3He reactions cross sections (expressed in terms of the astrophysical S -factor) with higher accuracy, and the electron screening effects in these reactions for different environments (insulators and metallic targets). The 7Li(p,α) 4He angular distributions were also measured. These measurementstook place in two laboratory facilities, in the framework of the LUNA (Laboratory for Undergroud Nuclear Astrophysics) international collaboration, namely the Laboratorio ´ de Feixe de Ioes ˜ in ITN (Instituto Tecnologico ´ e Nuclear) Sacavem, ´ Portugal, and the Dynamitron-TandemLaboratorium in Ruhr-Universitat¨ Bochum, Germany. The ITN target chamber was modified to measure these nuclear reactions, with the design and construction of new components, the addition of one turbomolecular pump and a cold finger. The 7Li(p,α) 4He and 6Li(p,α) 3He reactions were measured concurrently with seven and four targets, respectively. These targets were produced in order to obtain adequate and stable lithium depth profiles. In metallic environments, the measured electron screening potential energies are much higher than the predictions of atomic-physics models. The Debye screening model applied to the metallic conduction electrons is able to explain these high values. It is a simple model, but also very robust. Concerning primordial nucleosynthesis and stellar evolution models, these results are very important as they show that laboratory measurements are well controlled, and the model inputs from these cross sections are therefore correct. In this work the 7Li(p,p)7Li differential cross section was also measured, which is useful to describe the 7Li(p,α) 4He entrance channel.

Low-power 6-bit 1-GS/s two-channel pipeline ADC with open-loop amplification using amplifiers with local-feedback

IEEE International Symposium on Circuits and Systems, pp. 2258 – 2261, Seattle, EUA

Bio and magnetostratigraphy of two Lower Miocene sections, Tagus basin (Portugal)

The magnetostratigraphy of two sections in early Miocene marine deposits of the Tagus Basin is studied. Thermal demagnetization was used to isolate the primary component of magnetization for 45 samples from the Foz da Fonte section, and for 74 others from Trafaria section. The succession of the polarity zones found in these sections is tentatively correlated with the geomagnetic polarity time scale (GPTS) on the basis of the biostratigraphic data yielded by planktic Foraminifera. The planktic zones and magnetic polarities recognized in these sections can be adequately correlated with the part of the GPTS [table calibrated by BERGGRENET al. (1985)] corresponding to the Anomalies 6 and 5E (Foz da Fonte) and 5D (Trafaria). This correlations suggests ages between 19,35 and 18,14 Ma for Foz da Fonte section, and 17,90 to 16,98 Ma for Trafaria.

Miocene sediments from Foz da Fonte and Penedo sections (Lower Tagus basin): clay minerals and isotopic data

Eight depositional sequences (DS) delimited by regional disconformities had been recognized in the Miocene of Lisbon and Setúbal Peninsula areas. In the case of the western coast of the Setúbal Peninsula, outcrops consisting of Lower Burdigalian to Lower Tortonian sediments were studied. The stratigraphic zonography and the environmental considerations are mainly supported on data concerning to foraminifera, ostracoda, vertebrates and palynomorphs. The first mineralogical and geochemical data determined for Foz da Fonte, Penedo Sul and Penedo Norte sedimentary sequences are presented. These analytical data mainly correspond to the sediments' fine fractions. Mineralogical data are based on X-ray diffraction (XRD), carried out on both the less than 38 nm and 2 nm fractions. Qualitative and semi-quantitative determinations of clay and non-clay minerals were obtained for both fractions. The clay minerals assemblages complete the lithostratigraphic and paleoenvironmental data obtained by stratigraphic and palaeontological studies. Some palaeomagnetic and isotopic data are discussed and correlated with the mineralogical data. Multivariate data analysis (Principal Components Analysis) of the mineralogical data was carried out using both R-mode and Q-mode factor analysis.

High-resolution correlation of coastal cliff sections in the Lagos- Portimao Formation (Lower - Middle Miocene, central Algarve, Portugal)

This paper describes a high-resolution stratigraphic correlation scheme for the early to middle Miocene Lagos-Portimão Formation of central Algarve, southern Portugal. The Lagos Portimão-Formation of central Algarve is a 60 m thick package of horizontally bedded siliciclastics and carbonates. The bryozoan and mollusc dominated biofacies is typical of a shallow marine, warm-temperate climatic environment. We define four stratigraphic marker beds based on biofacies, lithology, and gamma-ray signatures. Marker bed 1 is a reddish shell bed composed predominantly of bivalve shells in various stages of fragmentation. Marker bed 2 is a fossiliferous sandstone / sandy rudstone characterized by bryozoan masses. Marker bed 3 is also a fossiliferous sandstone with abundant larger foraminifers and foliate bryozoans. Marker bed 4 is composed of three distinct layers; two fossiliferous sandstones with an intercalated shell bed. The upper sandstone unit displays thickets of the bryozoan Celleporaria palmate associated with the coral Culizia parasitica. This stratigraphic framework allows to correlate isolated outcrops within the stratigraphic context of the Lagos-Portimão Formation and to establish high resolution chronostratigraphic Sr-isotopic dating.

Simulation of the velocity field in compound channel flow using different closure models

1st European IAHR Congress,6-4 May, Edinburg, Scotland

Ultrasound velocity profile (UVP) measurements in shallow open-channel flows

1st European IAHR Congress, 6-4 May, Edinburgh, Scotland

Flow resistance in open-channel flows with mobile hydraulically rough beds

River Flow 2008, Vol.1

As crianças e a internet. Crianças e tweens, as redes sociais e as ferramentas interactivas em Portugal - uma análise do canal temático ‘DISNEY CHANNEL PORTUGAL’

Trabalho projecto de mestrado em Novos Media e Práticas Web

Electron impact ionization cross sections and analysis of X-ray spectra

A thesis submitted for the degree of Ph. D. in Physics

Coherent structures in open channel flows with bed load transport over an hydraulically rough bed

Dissertação para obtenção do Grau de Mestre em Engenharia Civil – Perfil de Estruturas

Energy-efficient diversity combining for different access schemes in a multi-path dispersive channel

Dissertação para obtenção do Grau de Doutor em Engenharia Electrotécnica e Computadores

Improvement of Lipton’s business model through wholesalers and traditional supermarkets channel

Field Lab in Entrepreneurial Innovative Ventures

Numerical modelling of compound channel flow

Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BD/64337/2009 ; projects PTDC/ECM/70652/2006, PTDC/ECM/117660/2010 and RECI/ECM-HID/0371/2012

How can Biotherm grow in the selective skincare channel in Portugal?

Branding Lab