Geology on the moons of Uranus

In January 1986 the spaceprobe Voyager-2 revealed details of the surfaces of the icy satellites of Uranus for the first time, including grabens, other faulted features, impact craters and possible ice flows. Despite their apparent similarity to some of the moons of Jupiter and Saturn, they highlight many new questions as to the evolution of, and interactions between, such bodies.     

Magnetic reconnection in high-temperature plasma of solar flares

Quasi-steady high-temperature current sheets are an energy source during the main or hot phase of solar flares. Such sheets are shown to be stabilized with respect to the tearing instability by a small transverse component of magnetic field existing in the sheets.     

A new approach to the librational solution in the Ideal Resonance Problem

The librational motion of the Ideal Resonance Problem (Garfinkel, 1966, Jupp, 1969) is treated through an initialnon-canonical transformation which, however, leaves the equations of motion in a quasi-canonical form, with Hamiltonian expressed in standard trigonometric functions amenable to traditional averaging techniques. The perturbed solutions, similarly expressed intrigonometric near-identity transformations, and their frequencies can be found to arbitrary order, with the elliptic integrals expected of the system introduced only in a final explicit quadrature for a Kepler-type equation in the angular variable. The specific transformations and resulting equations of motion are introduced, and explicit solutions for the original variables are found to second order, with mean motion accurate to fifth. Limitation of the present solution to the librational region, the extension of that solution to higher order, and observations on the form of the associated Hamiltonian are also discussed.     

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.     

Phase transitions in the ISM a source of dissipative behaviour

By considering a simple fluid model, we investigate the role of phase transitions in the ISM on the galaxy- scale gas dynamics. Cooling and heating timescales in the ISM are typically shorter than typical galactic rotation timescales, so the individual phases in the ISM can be assumed to be in temperature equilibrium with the radiation field. Using this approximation we can construct an equation of state which depends upon the average density and mass fractions in the individual phases. Previous studies suggest that there is an equilibrium phase fraction as a function of pressure. We incorporate evolution towards this equilibrium state as a relaxation term with a time to obtain equilibrium . We derive a condition in terms of a critical Mach number when one dimensional shocks should be continuous. For small values of the relaxation time we show that the relaxation term acts like a viscosity. We show with one dimensional simulations that increasing causes shocks to become smoother. This work suggests that phase changes can strongly effect the gas dynamics of the ISM across spiral arms and bars.     

The origin of polygonal troughs on the Northern Plains of Mars

Viking photographs have revealed extraordinary systems of crudely polygonal troughs in three different areas of the northern plains of Mars. Trough widths average 200–800 m and average trough spacing is 5–10 km. The widest troughs have flat floors and steep sides which suggest that they are either grabens or tension cracks which have been partially filled. The following three arguments support the garben interpretation: (1) Two clear examples of vertical offsets along trough walls indicate that the troughs formed by downdropping of the floors. (2) Troughs similar in scale and morphology to those of the Martian northern plains form concentric and radial patterns in the Caloris Basin on Mercury. Most likely, they are extensional fractures or grabens resulting from uplift of the basin floor (Strom et al., 1975). The Caloris analogy suggests that the troughs on Mars are similar tectonic features related either to uplift or expansion of the planet. Fourteen rose diagrams of trough azimuths in southeastern Acidalia Planita show that locally they exhibit preferred orientations roughly parallel to the topographic contours, but overall there is no strong regional pattern. (3) The scale of tension crack systems is limited by the depth of fracturing because the extent of stress relief perpendicular to a crack is proportional to the crack depth. Observations of terrestrial tension cracks suggest a lower limit on crack depths of about one-tenth of the average spacing. Thus, if the Martian troughs are tension cracks, they would be expected to have depths of at least 500–1000 m. Mechanical considerations indicate that it is difficult to generate such deep cracks by surficial tension due to thermal cooling and contraction in permafrost, desiccation, or cooling of lava flows. Deep-seated tension of tectonic origin generally results in normal faults and not tension cracks.     

Is there Aβ/L relation for any type of qso absorption line system?

The possible correlation noted between the intrinsic quasar luminosity and the absorption line expulsion velocity is re-examined using homogeneous data sets for metal and L only line systems. The method of analysis is chosen to enable any reasonable form of correlation to be found. No correlation is detected at a confidence level >10%.