Spiral Structures and Chaotic Scattering of Coorbital Satellites

The fractal nature of the transitions between two sets of orbits separated by heteroclinic or homoclinic orbits is well known. We analyze in detail this phenomenon in Hill's problem where one set of orbits corresponds to coorbital satellites exchanging semi-major axis after close encounter (horse-shoe orbits) and the other corresponds to orbits which do not exchange semi-major axis (passing-by orbits). With the help of a normalized approximation of the vicinity of unstable periodic orbits, we show that the fractal structure is intimately tied to a special spiral structure of the Poincaré maps. We show that each basin is composed of a few well behaved areas and of an infinity of intertwined tongues and subtongues winding around them. This behaviour is generic and is likely to be present in large classes of chaotic scattering problems.This revised version was published online in October 2005 with corrections to the Cover Date.     

A contribution to the parameterization of total radiation

Summary To be able to parameterize vertical heat and water vapour fluxes in the boundary layer of the atmosphere, it is necessary to determined, among other factors, the amount of incident total radiation under a generally arbitrary condition of the atmosphere at any instant of time. This paper deals with a simple model for computing the total radiation based on known solar elevation, total cloud cover and the atmospheric turbidity parameter. This variant of the model was formulated on the basis of a two-year series of total radiation observations made in the radiation network of the Czech Hydrometeorological Institute, and on the measurements and observations made at the observatory of the Institute of the Physics of the Atmosphere in Kopisty. An example of comparing the observed and theoretical values of total radiation will also be given.

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The methodology of quantification of volcanic explosions from broad-band seismic signals and its application to the 2004–2005 explosions at Volcán de Colima, Mexico

A methodology is proposed for the quantification of volcanic explosions based on three parameters derived from broad-band seismic signals: the counter force of the eruption F , the power of the explosion P and the duration of the upward movement of the gas slug in the conduit to the free surface of magma, D . This methodology was applied to the 2004–2005 sequence of explosions at Volcán de Colima, Mexico. The broad-band records of more than 100 explosive events were obtained at a distance of 4 km from the crater. We determined the counter force of the eruption by modelling the low-frequency impulse of the seismic records of 66 volcanic explosions and estimated the power of 116 explosions from the spectra of the high-frequency impulse. The power of Colima explosions spans five orders of magnitude; the counter force spans four orders of magnitude. We show that the power of a volcanic explosion is proportional to the counter force of the eruption. These parameters may be used for the elaboration of a scale of volcanic explosions.     

Optimisation procedure for choosing Cam clay parameters

This paper analyzes the application of a grid-search approach for the estimation of modified Cam clay parameters from triaxial tests. By means of the systematic sampling of the error, in addition to locating the area presenting the smallest error, its “roughness”, is also characterized. This is a valuable information to evaluate the quality of the identification that has been carried out. The methodology proposed here does not aspire to be “the solution” to the problem of parameter identification. The aim is simply to provide a tool which may aid users with criteria.     

Effect of plant growth on Pb and Zn geoaccumulation in 300-year-old mine tailings of Zacatecas,México

Concentrations of Pb and Zn, plant uptake of these metals, the influence of the plants’ growth on the physicochemical properties and metal concentrations in the tailings of an abandoned 300-year-old mine tailing dam in Zacatecas, Mexico were investigated. Tailings were found to be heavily contaminated, with average levels of 2621 ± 53 and 3827 ± 83 mg/kg for Pb and Zn, respectively (maximum concentrations of 8466 ± 116 and 12,475 ± 324 mg/kg, respectively), exceeding international standards. Though physico-chemical conditions (pH, conductivity, redox potential, moisture, organic matter, nitrate, nitrite, ammonium nitrogen, total nitrogen, phosphorus and sulfates) do not favor the development of vegetation, some plants have adapted to these adverse conditions. Moreover, there was a significant reduction of Pb and Zn concentration in the rhizosphere (between 10–78% for Pb and 18–62% for Zn, depending on plant species). Sporobolus airoides showed average biomass concentrations of 173 ± 2 and 313 ± 6 mg/kg, for Pb and Zn, respectively; which implies a risk for mobility and possible incorporation into the food chain. Barcleyanthus salicifolius, Asclepsias linaria and Cortaderia selloana on the other hand, showed average biomass concentrations of 28 ± 3 and 121 ± 5 mg/kg of Pb and Zn, respectively, thus representing a lower biomagnification risk. The effect of these plants to reduce metal concentrations in the rhizosphere, improve physico-chemical conditions in metal polluted substrates, but with limited metal accumulation in biomass, suggests that they can be evaluated for use in stabilizing metal polluted tailings.     

Surrogate-based parameter inference in debris flow model

This work tackles the problem of calibrating the unknown parameters of a debris flow model with the drawback that the information regarding the experimental data treatment and processing is not available. In particular, we focus on the evolution over time of the flow thickness of the debris with dam-break initial conditions. The proposed methodology consists of establishing an approximation of the numerical model using a polynomial chaos expansion that is used in place of the original model, saving computational burden. The values of the parameters are then inferred through a Bayesian approach with a particular focus on inference discrepancies that some of the important features predicted by the model exhibit. We build the model approximation using a preconditioned non-intrusive method and show that a suitable prior parameter distribution is critical to the construction of an accurate surrogate model. The results of the Bayesian inference suggest that utilizing directly the available experimental data could lead to incorrect conclusions, including the over-determination of parameters. To avoid such drawbacks, we propose to base the inference on few significant features extracted from the original data. Our experiments confirm the validity of this approach, and show that it does not lead to significant loss of information. It is further computationally more efficient than the direct approach, and can avoid the construction of an elaborate error model.     

Preliminary characterization of some Argentinean Artemia populations from La Pampa and Buenos Aires provinces

Artemia populations were sampled in four hypersaline ecosystems in continental evaporitic basins from the Argentinean provinces of La Pampa and Buenos Aires. Biometrics of cysts and nauplii were performed. The morphometrics of adult females under standard culture conditions, studied by multivariate discriminant analysis, provided evidence that these populations belonged to the speciesA. persimilis; this was further supported by cross-breeding tests established between one of these populations (Salinas Grandes de Hidalgo, province of La Pampa) and a population ofA. franciscana from San Francisco Bay (California, USA), which showed reproductive isolation and barriers to gene flow between both populations.