This thesis considers the use of two U-series nuclides – 231 Pa and 230 Th – as proxies for studying ocean circulation. A total of six water-column profiles of 231 Pa, 230 Th, and 232 Th have been measured from two regions of the southwestern Indian Ocean: the Madagascar and Mascarene Basins; and the southeastern continental margin of South Africa. Measurement by MC-ICP-MS of 10 litre water samples is possible for samples with as little as 4 and 2 fg of 231 Pa and 230 Th and yields typical uncertainties of 6% and 14% respectively. These profiles show that the scavenging and advection histories of water masses can affect their 231 Pa concentration, with distinct variations superimposed on a general increase in concentration with depth due to reversible scavenging. A 1D particle scavenging model is used to show that sedimentary (231 Paxs /230 Thxs )0 is most representative of the (231 Pa/230 Th) of the bottom most water mass at any one locality, although in turn this water mass (231 Pa/230 Th) will be dependent not only on its advection and scavenging history but also the 231 Pa and 230 Th concentrations of the overlying water masses during advection. Acknowledgment that sedimentary (231 Paxs /230 Thxs )0 is “set” by the bottommost water mass is important for interpretation of scenarios where changes in depth of circulation, as well as circulation strength, may have occurred. A record of sedimentary (231 Paxs /230 Thxs )0 has been recovered from a 6 m Kasten core from the Mascarene Basin covering the past 140 ka, in order to reconstruct flow of AABW into the basin. The (231 Paxs /230 Thxs )0 measured is below the production ration of 0.093 and shows no significant variation. This indicates that (231 Paxs /230 Thxs )0 is sensitive to changes in particle productivity and circulation at this location and that there has been little or no change in either environmental variable over the last full interglacial-glacial cycle. This finding is in contrast to other ocean basins, particularly the North Atlantic, where large changes in circulation are observed.

Spectroscopic orbital elements and/or related parameters have been determined for eight binary systems, using radial-velocity measurements that have a typical precision of about 15 ms⁻¹. The orbital periods of these systems range from about 10 days to 26 years, with a median of about 6 years. Orbital solutions were determined for the seven systems with shorter periods. The measurement of the mass ratio of the longest-period system, HD217166, demonstrates that this important astrophysical quantity can be estimated in a model-free manner with less than 10% of the orbital cycle observed spectroscopically.\\ Single-lined orbital solutions have been derived for five of the binaries. Two of these systems are astrometric binaries: β Ret and ν Oct. The other SB1 systems were 94 Aqr A, θ Ant, and the 10-day system, HD159656. The preliminary spectroscopic solution for θ Ant (P~18 years), is the first one derived for this system. The improvement to the precision achieved for the elements of the other four systems was typically between 1--2 orders of magnitude. The very high precision with which the spectroscopic solution for HD159656 has been measured should allow an investigation into possible apsidal motion in the near future. In addition to the variable radial velocity owing to its orbital motion, the K-giant, ν Oct, has been found to have an additional long-term irregular periodicity, attributed, for the time being, to the rotation of a large surface feature.\\ Double-lined solutions were obtained for HD206804 (K7V+K7V), which previously had two competing astrometric solutions but no spectroscopic solution, and a newly discovered seventh-magnitude system, HD181958 (F6V+F7V). This latter system has the distinction of having components and orbital characteristics whose study should be possible with present ground-based interferometers. All eight of the binary systems have had their mass ratio and the masses of their components estimated.\\ The following comments summarize the motivation for getting these results, and the manner in which the research was carried out. \\ The majority of stars exist in binary systems rather than singly as does the Sun. These systems provide astronomers with the most reliable and proven means to determine many of the fundamental properties of stars. One of these properties is the stellar mass, which is regarded as being the most important of all, since most other stellar characteristics are very sensitive to the mass. Therefore, empirical masses, combined with measurements of other stellar properties, such as radii and luminosities, are an excellent test for competing models of stellar structure and evolution.\\ Binary stars also provide opportunities to observe and investigate many extraordinary astrophysical processes that do not occur in isolated stars. These processes often arise as a result of direct and indirect interactions between the components, when they are sufficiently close to each other. Some of the interactions are relatively passive, such as the circularization of the mutual orbits, whilst others result from much more active processes, such as mass exchange leading to intense radiation emissions. \\ A complete understanding of a binary system's orbital characteristics, as well as the measurement of the all-important stellar masses, is almost always only achieved after the binary system has been studied using two or more complementary observing techniques. Two of the suitable techniques are astrometry and spectroscopy. In favourable circumstances, astrometry can deduce the angular dimensions of the orbit, the total mass of the system, and sometimes, its distance from us. Spectroscopy, on the other hand, can determine the linear scale of the orbit and the ratio of the stellar masses, based on the changing radial velocities of both stars. When a resolved astrometric orbital solution is also available, the velocities of both stars can allow the binary system's parallax to be determined, and the velocities of one star can provide a measure of the system mass ratio.\\ Unfortunately, relatively few binary systems are suited to these complementary studies. Underlying this difficulty are the facts that, typically, astrometrically-determined orbits favour those with periods of years or decades, whereas spectroscopic orbital solutions are more often measured for systems with periods of days to months. With the development of high-resolution astrometric and spectroscopic techniques in recent years, it is hoped that many more binary systems will be amenable to these complementary strategies.\\ Several months after this thesis began, a high-resolution spectrograph, HERCULES, commenced operations at the Mt John University Observatory, to be used in conjuction with the 1-metre McLellan telescope. For late-type stars, the anticipated velocity precision was ≲10 ms⁻¹. The primary goals of this thesis were: 1.~to assess the performance of HERCULES and the related reduction software that subsequently followed, 2.~to carry out an observational programme of 20 or so binary systems, and 3.~to determine the orbital and stellar parameters which characterize some of these systems. The particular focus was on those binaries that have resolved or unresolved astrometric orbital solutions, which therefore may be suited to complementary investigations.\\ HERCULES was used to acquire spectra of the programme stars, usually every few weeks, over a timespan of about three years. High-resolution spectra were acquired for the purpose of measuring precise radial velocities of the stars. When possible, orbital solutions were derived from these velocities, using the method of differential corrections.

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Made available in DSpace on 2014-10-09T12:28:38Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:15Z (GMT). No. of bitstreams: 0 / Neste trabalho foram determinadas as concentrações dos radionuclídeos naturais 226Ra, 232Th e 40K em amostras de areias superficiais para 16 localizações ao longo da costa da Grande Vitória, região metropolitana do estado do Espírito Santo, sudeste do Brasil. As áreas de estudo compreendem as praias de Manguinhos e Jacaraípe no município da Serra, Camburi, Praia do Canto e Curva da Jurema no município de Vitória, Praia da Costa e Praia de Itapuã no município de Vila Velha, Praia de Setibão, Setibinha, Praia do Morro, Praia das Castanheiras e Praia da Areia Preta no Município de Guarapari e areia da Reserva Paulo Cesar Vinha também localizada no município de Guarapari. Para cada sítio de estudo, três amostras foram seladas em frascos de 100 ml de polietileno de alta densidade. Após espera de aproximadamente 4 semanas para atingir o equilíbrio secular das séries do 238U e 232Th, as amostras foram medidas por espectrometria gama de alta resolução e o espectro analisado com o software WinnerGamma. A correção da auto-absorção foi realizada para todas as amostras. A concentração do 226Ra foi determinada pela média ponderada das concentrações do 214Pb e 214Bi, a concentração de 232Th pela média ponderada das concentrações dos 228Ac, 212Pb e 212Bi e a concentração de 40K pela sua transição única de 1460 keV. O equivalente em rádio e o índice gama foram obtidos a partir das concentrações de 226Ra, 232Th e 40K. As concentrações de 226Ra variaram de 3 ± 1Bq.kg-1 a 738 ± 38Bq.kg-1, com o maior valor na localidade central da Praia de Camburi. As concentrações de 232Th variaram de 7 ± 3Bq.kg-1 a 7422 ± 526Bq.kg-1, com o maior valor na Praia da Areia Preta. As concentrações de 40K variaram de 14 ± 6Bq.kg-1 a 638 ± 232Bq.kg-1, com o maior valor na Praia da Areia Preta. O cálculo do equivalente em rádio e do índice gama mostrou duas faixas distintas. Na primeira, para a maioria das praias, o equivalente em rádio variou de 15 ± 6Bq.kg-1 a 257 ± 18Bq.kg-1, abaixo do limite inferior de 370Bq.kg-1 recomendado pela OECD como adequado para uso em material de construção e o índice gama externo foi inferior ao limite aceitável de 1 sugerido pelo UNSCEAR. Na segunda, para as praias de Setibinha, Curva da Jurema, Camburi Sul e Camburi Central e Praia da Areia Preta, o equivalente em rádio variou de 820 ± 40Bq.kg-1 até 11200 ± 580Bq.kg-1, excedendo de 2 a 30 vezes o limite mínimo recomendado para aplicação na construção civil e o índice gama superou de 3 até quase 40 vezes o limite sugerido pelo UNSCEAR. / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP