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Organic conductors and superconductors
No full textInternational audienceThis review attempts to present the most salient developments of research on organic conductors and superconductors during the past 10 years. A theoretical introduction treats instabilities of quasi-one-dimensional electron systems and associated precursor e ects which are relevant to the experimental results on organic conductors. We then describe the characterization of quasi-one-dimensional organic conductors by their transport, optical and magnetic properties. Finally, two sections are devoted to the experimental investigation of the low temperature instabilities: lattice instability in TTF±TCNQ and related compounds, superconducting or antiferromagnetic instabilities in the (TMTSF) 2 X series. The importance of one-dimensional ¯uctuations is emphasized in both lattice and superconducting instabilities. Contents page* This article was originally published in Advances in Physics, volume 31, 1982. It had attracted 663 citations by October 2001, and is ranked 23 in the index of articles attracting more than 100 citations.} References are given separately within each section and will be found at the end of the corresponding section.} References are given separately within each section and will be found at the end of the corresponding section.</div
Dealing with spatial heterogeneity
No full textInternational audienceHeterogeneity can be dealt with by defining homogeneous equivalent properties, known as averaging, or by trying to describe the spatial variability of the rock properties from geologic observations and local measurements. The techniques available for these descriptions are mostly continuous Geostatistical models, or discontinuous facies models such as the Boolean, Indicator or Gaussian-Threshold models and the Markov chain model. These facies models are better suited to treating issues of rock strata connectivity, e.g. buried high permeability channels or low permeability barriers, which greatly affect flow and, above all, transport in aquifers. Genetic models provide new ways to incorporate more geology into the facies description, an approach that has been well developed in the oil industry, but not enough in hydrogeology. The conclusion is that future work should be focused on improving the facies models, comparing them, and designing new in situ testing procedures (including geophysics) that would help identify the facies geometry and properties. A world-wide catalog of aquifer facies geometry and properties, which could combine site genesis and description with methods used to assess the system, would be of great value for practical applications
