Eddy Detection Over Southern Indian Ocean Using TOPEX/POSEIDON Altimeter Data

Field biological and geomorphological observations in certain East Asia coasts permit definition of Mean Sea Level (MSL) with an accuracy of ～10 cm, that is, a vertical geodetic datum, as well as recognition of the MSL of fossil shorelines, up to a few thousand years old, mainly associated with tectonic/seismic effects. Subsidence produced by compaction of nearly-surficial strata seems also to be a usual effect. These data indicate that datum variability is a widespread effect in East Asia, time-dependent even at time scales affecting engineering works, but only in a few cases fully predictable.     

Evidence for sinistral strike-slip deformation in The Solomon Island arc

During the SOPACMAPS 2 crusie carried out by IFREMER (Institut Français de Recherche pour l'Exploitation de la Mer) and ORSTOM (Institut Français de Recherche Scientifique pour le dévelopement en Coopération) on theR/V L'Atalante, in the Central Solomon Arc area, multibeam bathymetric and imagery data and single-channel seismic reflection profiles were collected from an area of about 3500 km², to evaluate regional tectonics. Structural data geophysical profiles interpretation provide evidence for left-lateral transtensional tectonics on the southern edge of the Central Solomon Trough. This transtensional deformation is represented by faulting, block tilting, and rhombohedral deformation. The regional geology and the analysis of the sedimentary cover allow us to demonstrate that this tectonic occurred in two different phases during Oligocene to Miocene and Pliocene to Pleistocene times.     

Irrigation-induced loess flow failure in Heifangtai Platform,North-West China

Because the construction of dams and hydro-electric power stations of Liujiaxia and Yanguoxia across the Yellow River in West Gansu Province, North-West China, inhabitants in the reservoir areas were resettled in Heifangtai Loess Platform. Irrigation thus started in 1968. Perched water table was significantly raised and resulted in many loess flow failures in the past 30 years. This type of landslide was often featured by long runout distance, high speed and recurrence. Laboratory tests along ICU and CSD stress paths were performed. It is shown that the loess has a strong strain-softening behavior and instability can occur in drained condition before undrained liquefaction. The failure mechanism of loess flow can be interpreted as the following process: with increasing perched water table, collapse in loess was first triggered in drained condition and led to undrained loading to adjacent soil in the lower saturated part of the loess platform. Under gravity loading applied by upper dry loess, undrained flow failure mobilized, eventually.     

The development and structure of bright active regions at 2.8 cm

The development of three intense active centers during their appearance on the solar disk is examined using high resolution observations at 2.8 cm. Each region shows a very bright component with brightness temperature > 10⁶ K and size smaller than 20.The development of the bright components have been investigated on different time scales. Intensity fluctuations on a time scale of minutes are within the instrumental accuracy while the evolution over periods of days shows a variation of the flux density up to 30–40% per day.The problem of the bright cores height is discussed. Heights within 10 × 10³ and 40 × 10³ km are found using their apparent displacement on the disk.     

Diffusion in momentum space as a picture of second-order Fermi acceleration

Energetic particles in a turbulent medium can be subject to second-order Fermi acceleration due to scattering on moving plasma waves. This mechanism leads to growing particle momentum dispersion and, at the same time, increases the mean particle energy. In the most frequently met situations both processes can be represented by a single momentum diffusion term in the particle kinetic equation. In the present paper we discuss the conditions allowing the additional term for regular acceleration to arise. For forward-backward asymmetric scattering centres, besides the diffusive term one should explicitly consider the regular acceleration term in momentum space, which can consist of the first-order (∝ V), as well as the second-order (∝ V²) part in the wave velocity V. We derive the condition for the scattering probability in the wave rest frame requied for vanishing the regular acceleration term and provide a simple mechanical example illustrating the theoretical concepts. Finally, we address its possible role in cosmic ray acceleration processes.     

Determining the interstellar extinction and distances for Galactic novae

Using photometric data for Galactic novae, we compared the Sharov (1963) and Schlegel et al. (1998) interstellar extinction maps. We found the distances and extinctions for 64 novae.     

Short time-scale fluctuations in the difference light curves of QSO 0957+561A,B: microlensing or noise?

From optical R -band data of the double quasar QSO 0957+561A,B, we made two new difference light curves (with an overlap of about 330 d between the time-shifted light curve for the A image and the magnitude-shifted light curve for the B image). We observed noisy behaviours around the zero line and no short time-scale events (with a duration of months), where the term 'event' refers to a prominent feature that may be a result of microlensing or another source of variability. Only one event lasting two weeks and rising −33 mmag was found . Measured constraints on the possible microlensing variability can be used to obtain information on the granularity of the dark matter in the main lensing galaxy and the size of the source. In addition, one can also test the ability of the observational noise to cause the rms averages and the local features of the difference signals. We focused on this last issue. The combined photometries were related to a process consisting of an intrinsic signal plus a Gaussian observational noise. The intrinsic signal has been assumed to be either a smooth function (polynomial), a smooth function plus a stationary noise process, or a correlated stationary process . Using these three pictures without microlensing, we derived some models totally consistent with the observations. We finally discussed the sensitivity of our telescope (at Teide Observatory) to several classes of microlensing variability.     

Combustion as the cause of comet P/Halley's activity

The totality of the results obtained in the VEGA, GIOTTO and SUISEI projects does not lend itself to interpretation within the old sublimation models of comet activity considering solar radiation as the sole source of energy. Among them are the systematic excess of the velocity and temperature of the gas escaping from the nucleus over the theoretical values, the outflow being concentrated in several ( ~ 12–15) narrow ( ~ 300 m in size at the nucleus) hypersonic jets carrying very large amounts of remarkably fine CHON dust and located along continuous lines on the nuclear surface, intense release from the nucleus or very close to it (2 × 10³km) of CO (Q _Co/Q _{H2 O} = 0.05–0.2) with a smaller amount of CO₂ (Q _{CO 2}/ Q _{H2 O} 0.015), large near-nucleus abundances of C, C⁺ (Q _C/Q _CO 0.29), etc.The new observations, together with some earlier data still poorly understood (e.g. the appearance in the coma of large amounts of C₃) can be accounted for by assuming the cometary ices to contain, apart from hydrocarbons, nitrogen-containing compounds, etc. also of free oxygen ( ~ 15 wt.%). Under these conditions, burning should occur in the products of sublimation under deficiency of oxidizer accompanied by the production of soot, smoke, etc. The burning should propagate under the surface crust and localize primarily at a few sites.The presence of oxygen in cometary ices follows from a new eruption theory assuming the minor bodies of the Solar System to have formed in explosions of the massive ice envelopes saturated by electrolysis products on distant moonlike bodies of the type of Ganymede and Callisto.     

Spatial variation of seismic motion induced by propagation of body waves

Spatial variation of earthquake ground motion is an important phenomenon that cannot be ignored in the design and safety of strategic structures. Several models have been developed to describe this variation using statistical, mathematical or physical approaches. The latter approach is not specific to an event. A recent contribution, which uses such an approach and called complete stochastic deamplification approach (CSDA), was developed [1]. The aim of this paper is to analyze the spatial variation of earthquake motion induced by the propagation of body waves using the CSDA. Coherency functions are evaluated for the cases of SH–SV–P waves propagating through stratified soil. Results obtained show that the variation of the coherency function is not the same for vertical and horizontal components and that the motion is more coherent at depth than at the free surface. In fact, we found that the rate of decrease with frequency and distance is not the same if P–SV waves propagate through stratified soil.