VIRGO: Experiment for helioseismology and solar irradiance monitoring

The scientific objective of the VIRGO experiment (Variability of solar IRradiance and Gravity Oscillations) is to determine the characteristics of pressure and internal gravity oscillations by observing irradiance and radiance variations, to measure the solar total and spectral irradiance and to quantify their variability over periods of days to the duration of the mission. With these data helioseismological methods can be used to probe the solar interior. Certain characteristics of convection and its interaction with magnetic fields, related to, for example, activity, will be studied from the results of the irradiance monitoring and from the comparison of amplitudes and phases of the oscillations as manifest in brightness from VIRGO, in velocity from GOLF, and in both velocity and continuum intensity from SOI/MDI. The VIRGO experiment contains two different active-cavity radiometers for monitoring the solar constant, two three-channel sunphotometers (SPM) for the measurement of the spectral irradiance at 402, 500 and 862 nm, and a low-resolution imager (LOI) with 12 pixels, for the measurement of the radiance distribution over the solar disk at 500 um. In this paper the scientific objectives of VIRGO are presented, the instruments and the data acquisition and control system are described in detail, and their measured performance is given.died 13 October 1994     

Effective two-phase flow through highly heterogeneous porous media: Capillary nonequilibrium effects

We consider the two-phase flow through a dual-porosity medium, characterized by a period of heterogeneity ω, a ratio of global permeabilities ∈_K, and a ratio of the order of capillary forces ∈_c. The limit when ω tends to zero at different values of ∈_K and ∈_c gives four classes of global behavior, differing by the type of elementary flows at the one-cell level. We propose a diagram of their predominance. A macro-scale model is constructed by formal homogenization techniques for one of these classes; it shows a nonlinear kinetic relationship for the averaged capillary pressure functions, and leads to a decomposition for the effective phase permeability tensors. A capillary relaxation time is explicitly determined. This revised version was published online in August 2006 with corrections to the Cover Date.     

Abundance of organic compounds photochemically produced in the atmospheres of the outer planets

Organic photochemical syntheses in the Jovian atmosphere were simulated by irradiating, at 147 nm, gaseous mixtures of methane and ammonia with varying quantities of hydrogen. An excess of H₂ did not eliminate organic synthesis but did affect the yields quantitatively and qualitatively.     

Hydrogeological modeling of radionuclide transport in low permeability media: a comparison between Boom Clay and Ypresian Clay

Deep low-permeability clay layers are considered as suitable environments for disposal of high-level radioactive waste. In Belgium, the Boom Clay is the reference host formation and the Ypresian Clay an alternative host formation for research and safety and feasibility assessment of deep disposal of nuclear waste. In this study, two hydrogeological models are built to calculate the radionuclide fluxes that would migrate from a potential repository through these two clay formations. Transport parameter heterogeneity is incorporated in the models using geostatistical co-simulations of hydraulic conductivity, diffusion coefficient and diffusion accessible porosity. The calculated radionuclide fluxes in the two clay formations are compared. The results show that in the Ypresian Clay larger differences between the fluxes through the lower and the upper clay boundary occur, larger total output radionuclide amounts are calculated and a larger effect of parameter heterogeneity on the calculated fluxes is observed, compared to the Boom Clay.     

Periodicity of Element Changes in the Upper Devonian Strata of Dachang Area,Southern China—A Case Study of Spectral Analysis

Power spectral analysis is discussed and an exmple of its application to a geochemical stratigraphic profile is presented.In the Dachang area,all major elements,as well as the maximal sedimentary trend factor(MSTF),demonstrate consistent change periodicity,but are out-of-step with cach other.This can be explained by sedimentogecochemical consideration.The results of power spectral analysis enable geochemists to group elements on the basis of the distribution of their changed periods,and to interpret some special geological and geochemical situations.     

Jurassic lagoonal environments and quasi-abiotic platy limestone accumulation: microbial interventions

Within the regressive sequence (eustatic sea-level fall) that characterizes the French Southern Jura carbonate platform during the Kimmeridgian, a succession of three facies (called here units 1–3) may be observed in a palaeolagoon near Orbagnoux. Unit 1 is a shallow-water, intensely burrowed, carbonate deposit; unit 2 (consisting of laminated, organic matter-rich carbonate) represents a shallow lagoonal environment, prone to stromatolite development and organic matter accumulation; unit 3 consists of platy limestones almost devoid of identifiable biota. Trace element distributions indicate that depositional and early diagenetic conditions must have been reducing during deposition of unit 1 and, especially, unit 2, whereas they were much less reducing during deposition of unit 3. However, the latter does not contain body or trace fossils, with the exception of structures interpreted as calcified bacteria. The reasons why the apparently normal marine environment of unit 3 did not allow a normal biota to develop are explored and lead us to propose that: (i) unit 2 may be a Jurassic counterpart of modern kopara deposits (stromatolites of French Polynesian atolls); and (ii) unit 3 may be the result of palaeokopara reworking. This model invokes the extensive intervention of microbes in the formation of these carbonate deposits.