Sea-structure interaction for tripod-type steel gravity platform

The paper deals with a numerical integrated procedure to calculate the effects of the interaction between sea waves and a tripod-type steel gravity platform. The main aspects to be taken into account for a reliable wave loading analysis of such a new type of platform are emphasized. Among them, the field perturbation effect due to the large bodies presence is analysed. Finally, some principal results in terms of structure global loads obtained by the numerical integrated procedure are presented.     

Harpacticoida taxocen diversity in the silty-sandy littoral zone of Kandalaksha Bay of the White Sea

The fauna composition, ecological groups, and life forms of Harpacticoids of soft littoral grounds from 15 sites off the Karelian coast in Kandalaksha Bay of the White Sea were studied. Six types of harpacticoid taxocens with different sets of dominating species are described. On silty sands with clear signs of desalination, the Stenchelia palustris taxocen is common; medium-grained sands are characterized by the Heterolaophonte minuta, Paraleptastacus kliei — Huntemannia jadensis, and Amphiascoides nanus — Scottopsyllus minor taxocens; while on coarse sands, the Ameira parvula and Ameira scotti — Mesochra lilljeborgi taxocens have developed. The diversity of the taxocens is partly explained by the differences in the grain-size composition and salinity at different sites. In addition, groups of various taxocens dwelling on the same type of the sediments were found in different minor bights of the coastline.     

Regional tectonic trends on the inner continental shelf off Konkan and Central West Coast of India

Satellite imagery and offshore magnetic data were analysed to correlate regional tectonic elements on the inner continental shelf off Konkan and the adjacent Deccan plateau. Three statistically important lineament trends—N-S, WNW-ESE and ENE-WSW—that prevail on land are correlatable well with the offshore trends. This positive correlation suggests simultaneous deformation. The major magnetic lineament observed off Jaigad Bay, west coast of India, may be the extension of onshore lineaments. The correlation of both the offshore and onshore trends indicates that the fracture pattern of the crystalline basement has also controlled the offshore structural pattern.     

Cometary collisions and the dark material on Iapetus

Iapetus (S8) is unique in our solar system in that the albedo of its leading hemisphere is only 0.05 while that of the trailing side is 0.5. Several existing hypotheses are examined and found inadequate. Photometric studies of the dark side are compared to comet nuclei and class D asteroids. It is hypothesized that in the last 10⁶–10⁸ yrs the leading side suffered a high-velocity collision with a cometary body of mass 10¹³–10¹⁵ kg and traveling at a speed of 20 km s^–1. About 5–16% of the excavated material was ejected into space, where the vaporized ices dissipated while the dark carbonaceous/silicate material was reaccreted on the leading side. The collision, although not sufficient to break Iapetus' tidal lock, resulted in a period of oscillation of about 5 yr. Until tidal friction reasserted a lock, the oscillation gave rise to the longitude effect, viz., the observed fact that the dark material covers more than 220 of longitude but only 110 of latitude.     

Interpretation of a special fine structure in type-IV solar radio bursts

A special fine structure (slowly drifting chains of narrowband fiber bursts), firstly observed during the solar type-IV radio burst on April 24, 1985, is interpreted as the radio signature of whistler waves periodically excited by a switch-on/switch-off process of a loss-cone instability in a localized wave packet of the fast magnetoacoustic mode.     

The eruption of a quiescent prominence as observed in UV lines

We compare observations of an eruptive and a quiescent prominence in order to better understand the energetic processes in an eruptive prominence. Observations of an eruptive prominence were obtained in H, several UV emission lines (1215–1640 Å), and coronal white light at approximately 19:00 UT on September 20, 1980. The data we present shows the development of the eruption in the H and UV emission lines and is compared with the intensities from similar observations of a quiescent prominence. While the event is coincident with some coronal changes, above 1.2 and up to 1.5 solar radii, it does not result in a true coronal mass ejection event.The comparison between the eruptive and quiescent prominences reveals several differences which suggest that the activation consists not only of a mechanical movement of material, but also changes in the temperature of the prominence plasma. Some prominence material that does not seem to participate in the large scale prominence motion is heated during the eruptive event. Most of this material is heated to transition zone temperatures with almost no cool core (i.e., no or very little H emission). The behavior indicates that there are structures that are first cool and then heat up to transition zone temperatures (apparently remaining stable for some time at these temperatures). Since this is an unstable temperature region for prominence type structures the energy transport that allows this is not understood and presents an interesting theoretical problem.Member of the Carrera del Investigador, CONICET, Argentina, presently at The University of Alabama in Huntsville.