Tidal friction in close-in satellites and exoplanets. The Darwin theory re-visited

This report is a review of Darwin's classical theory of bodily tides in which we present the analytical expressions for the orbital and rotational evolution of the bodies and for the energy dissipation rates due to their tidal interaction. General formulas are given which do not depend on any assumption linking the tidal lags to the frequencies of the corresponding tidal waves (except that equal frequency harmonics are assumed to span equal lags). Emphasis is given to the cases of companions having reached one of the two possible final states: (1) the super-synchronous stationary rotation resulting from the vanishing of the average tidal torque; (2) the capture into a 1:1 spin-orbit resonance (true synchronization). In these cases, the energy dissipation is controlled by the tidal harmonic with period equal to the orbital period (instead of the semi-diurnal tide) and the singularity due to the vanishing of the geometric phase lag does not exist. It is also shown that the true synchronization with non-zero eccentricity is only possible if an extra torque exists opposite to the tidal torque. The theory is developed assuming that this additional torque is produced by an equatorial permanent asymmetry in the companion. The results are model-dependent and the theory is developed only to the second degree in eccentricity and inclination (obliquity). It can easily be extended to higher orders, but formal accuracy will not be a real improvement as long as the physics of the processes leading to tidal lags is not better known.Comment: 30 pages, 7 figures, corrected typo

Silicate alteration mechanisms

Transmission electron microscopy shows that mineral alteration mechanisms are at least partly controlled by the structure of the altering mineral. Silicates of Fe and Mg with extended sequences of metal-oxygen octahedra change to trioctahedral layer-silicates showing a preferred orientation to the original mineral. Olivine, pyroxene, and biotite conform to this scheme, their alteration products inherit much of their structure. By contrast, framework silicates (which have tetrahedral Al) contribute little of their structure directly to clay-minerals, and alter via an amorphous phase to dioctahedral layer silicates.La microscopie électronique à transmission montre que les mécanismes d'altération des minéraux sont contrôlés, du moins jusqu'à un certain degré, par la structure du minéral qui subit l'altération. Les silicates de Fe et Mg avec des séquences étendues d'octaèdres à métaux et oxygène se changent en silicate phylliteux triocta-édriques,qui montrent une orientation préférentielle par rapport au minéral originel L'olivine, le pyroxene et la biotite se conforment à ce système ; les produits issus de leur altération héritent d'une grande partie de leur structure. Par contraste, les fedspaths et minéraux associés (qui contiennent de l'Ai tétraédrique) ne contri¬ buent que très peu par leur structure aux minéraux argileux, et s'altèrent à travers une phase amorphe pour devenir des silicates phylliteux dioctaédriques .Eggleton R.A, Smith K. L. Silicate alteration mechanisms. In: Pétrologie des altérations et des sols. Vol. I : Pétrologie expérimentale. Colloque international du CNRS, Paris 4-7 juillet 1983. Strasbourg : Institut de Géologie – Université Louis-Pasteur, 1983. pp. 45-53. (Sciences Géologiques. Mémoire, 71

Frequência e riqueza de cupins em áreas de plantio de eucalipto no litoral norte da Bahia

O objetivo deste trabalho foi avaliar a frequência e a riqueza de espécies de cupins que ocorrem em áreas de reflorestamento com eucalipto. As amostras foram coletadas em três áreas de Eucalyptus recém-colhido, em dezembro de 2005, por meio de seis transectos de 100 m de comprimento por 2-m de largura, subdivididos em 20 parcelas (2x5 m) contíguas. Cada parcela foi amostrada por uma hora por pessoa, e de cada subdivisão foram retiradas 12 amostras de 20x20x20 cm de profundidade, das quais foram coletadas 21-espécies de cupins, pertencentes a duas famílias e 16 gêneros. Dez espécies foram consideradas dominantes, todas da família Termitidae, das quais as de maior frequência foram Amitermes amifer e Nasutitermes corniger. O grupo funcional xilófago teve o maior número de espécies (11) e a maior frequência. Espécies conhecidas como pragas em eucalipto tiveram frequência abaixo do limite de dominânci

Logging cuts the functional importance of invertebrates in tropical rainforest

Invertebrates are dominant species in primary tropical rainforests, where their abundance and diversity contributes to the functioning and resilience of these globally important ecosystems. However, more than one-third of tropical forests have been logged, with dramatic impacts on rainforest biodiversity that may disrupt key ecosystem processes. We find that the contribution of invertebrates to three ecosystem processes operating at three trophic levels (litter decomposition, seed predation and removal, and invertebrate predation) is reduced by up to one-half following logging. These changes are associated with decreased abundance of key functional groups of termites, ants, beetles and earthworms, and an increase in the abundance of small mammals, amphibians and insectivorous birds in logged relative to primary forest. Our results suggest that ecosystem processes themselves have considerable resilience to logging, but the consistent decline of invertebrate functional importance is indicative of a human-induced shift in how these ecological processes operate in tropical rainforests