Identification des anomalies magnétiques sur les dorsales à faible taux d'expansion: Méthode des taux fictifs

The fit between calculated and observed magnetic anomalies from slow-spreading centers is improved when allowing for a transition zone between two inversely magnetized blocks. In this paper it is shown that these models are very easily computed by choosing a fictitious spreading rate which is slower than the real spreading rate and by changing the distance scale appropriately. With these slow fictitious spreading rates, the models are very sensitive to the relative position of the successive inversions and could be used to adjust these positions in the magnetic time scales.     

Studies of Hydrochemical and Kinetic Characteristics of Small Water Bodies in the Context of Their Eutrophication

Comparison study data on the hydrochemical parameters, bacterio- and phytoplankton, and reduction–oxidation characteristics of two ponds in Krasnoyarsk are presented. These water bodies are of interest due to the fact that the ecosystems of these natural model objects respond to eutrophication in different ways. It is assumed that the reason for this difference is in the hydrophysical characteristics depending on the morphology of the basins of the water bodies rather than in the hydrochemical characteristics.     

Analysis of Numerical Procedures for Solving Mass Transport Problems at a Regional Scale

The principal mass transport models and the ways of their implementation are considered. Some problems associated with the application of numerical methods for mass transport modeling in problems of dissolved chemicals migration at a regional scale are discussed. A new method proposed in this study allows the determination of the space structure of a groundwater flow and the simulation of steady-state convective mass transport.     

Problems associated with direct displacement-based design of concrete bridges with single-column piers, and some suggested improvements

Currently available displacement-based design (DBD) procedures for bridges are critically evaluated with a view to identifying extensions and/or modifications of the procedure, for it to be applicable to final design of a fairly broad class of bridges. An improved direct DBD procedure is presented, including a suite of comprehensive design criteria and proper consideration of the degree of fixity of the pier top. The design of an overpass bridge (originally designed to a current European Code), applying the improved ‘direct’ displacement-based design (DDBD) procedure is presented and both ‘conventional’ and displacement-based designs are assessed using non-linear response-history analysis (NLRHA); comparisons are made in terms of both economy and seismic performance of the different designs. It is seen that DDBD provided a more rational base shear distribution among piers and abutments when compared to the force-based design procedure and adequately captured the displacement pattern, closely matching the results of the more rigorous NLRHA.     

Ionospheric disturbances in the years of solar activity minimum and their influence on HF radiowave propagation

The oblique sounding data at the Magadan-Irkutsk and Norilsk-Irkutsk paths together with the vertical sounding at stations located in northeastern Russia were used to analyze ionospheric disturbances in September 2005 and during geophysically active period in December 2006. It is found that during the main phase of magnetic storms, wave disturbances with a period of 2–4 h are registered. These disturbances cause variations in the layer maximum height up to 40–100 km and in the critical frequency up to 1.5–2 MHz. Those variations change substantially values of the maximum observed frequencies (MOF) of the ionospheric radio channel at the paths considered. Such wave disturbances can be caused by generation of AGWs in the auroral zone and their propagation to equatorial latitudes.     

Improved Resolution of Ambient Flow through Fractured Rock with Temperature Logs

In contaminant hydrogeology, investigations at fractured rock sites are typically undertaken to improve understanding of the fracture networks and associated groundwater flow that govern past and/or future contaminant transport. Conventional hydrogeologic, geophysical, and hydrophysical techniques used to develop a conceptual model are often implemented in open boreholes under conditions of cross-connected flow. A new approach using high-resolution temperature (±0.001°C) profiles measured within static water columns of boreholes sealed using continuous, water-inflated, flexible liners (FLUTe™) identifies hydraulically active fractures under ambient (natural) groundwater flow conditions. The value of this approach is assessed by comparisons of temperature profiles from holes (100 to 200 m deep) with and without liners at four contaminated sites with distinctly different hydrogeologic conditions. The results from the lined holes consistently show many more hydraulically active fractures than the open-hole profiles, in which the influence of vertical flow through the borehole between a few fractures masks important intermediary flow zones. Temperature measurements in temporarily sealed boreholes not only improve the sensitivity and accuracy of identifying hydraulically active fractures under ambient conditions but also offer new insights regarding previously unresolvable flow distributions in fractured rock systems, while leaving the borehole available for other forms of testing and monitoring device installation.