Generalized plasticity state parameter‐based model for saturated and unsaturated soils. Part 1: Saturated state

The behavior of granular materials is known to depend on its loose or dense nature, which in turns depends both on density and confining pressure. Many models developed in the past require the use of different sets of constitutive parameters for the same material under different confining pressures. The purpose of this paper is to extend a basic generalized plasticity model for sands proposed by Pastor, Zienkiewicz and Chan by modifying the main ingredients of the model flow—rule, loading–unloading discriminating direction and plastic modulus—to include a dependency on the state parameter. The proposed model is tested against the available experimental data on three different sands, using for each of them a single set of material parameters, finding a reasonably good agreement between experiments and predictions. Copyright © 2010 John Wiley & Sons, Ltd.     

Central Paratethys paleoenvironment during the Badenian (Middle Miocene): evidence from foraminifera and stable isotope (δ<Superscript>13</Superscript>C and δ<Superscript>18</Superscript>O) study in the Vienna Basin (Slovakia)

Stable isotope data of the foraminiferal carbonate shells and bulk sediment samples from the Central Paratethys were investigated to contribute to better knowledge of the paleoenvironmental changes in Badenian (Middle Miocene). Five benthic (Uvigerina semiornata, U. aculeata, Ammonia beccarii, Elphidium sp. and Heterolepa dutemplei) and three planktonic taxa (Globigerina bulloides, G. diplostoma and Globigerinoides trilobus), characterising the bottom, intermediate and superficial layers of the water column, were selected from the Vienna Basin (W Slovakia). The foraminiferal fauna and its isotope signal point out to temperature-stratified, nutrient-rich and consequently less-oxygenated marine water during the Middle/Late Badenian. Negative carbon isotope ratios indicate increased input of ¹²C-enriched organic matter to the bottom of the Vienna Basin. Positive benthic δ¹⁸O implies that the global cooling tendency recorded in the Middle Miocene has also affected the intramountain Vienna Basin. In this time, the Central Paratethys has been in the process of isolation. Our stable isotope trend suggests that the communication with Mediterranean Sea has been still more or less active on the south of Vienna Basin (Slovak part) in the Late Badenian, whereas the seawater exchange towards north was apparently reduced already during the Middle Badenian.     

Decay rates of sunspot groups from 1874 to 1976

The global behaviour and fine structure of the distribution of sunspot decay rates from activity cycle 13 to 20 are presented. It is shown that the distribution of this parameter is lognormal. Statistically significantly lower values of decay rates are found in cycles 13, 14, and 18 for isolated spots. The complex groups had no appreciable changes.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Photometry of AR Lac

Visible photometry of the RS CVn system AR Lac is presented. We find some interesting features in the light curves. Also a possible oscillation with period 1.05 hr arises from the data. A new determination of the geometrical parameters of the system is given.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Velocity fields associated with the magnetic component of solar faculae

The StokesV asymmetries observed in solar faculae can be interpreted by invoking the presence of magnetic and velocity fields variations along the line-of-sight. By means of a perturbative approach, we develop the theoretical dependence on magnetic and velocity fields of the StokesV profile around its zero-crossing point. We find that the empirical curves of growth for theV zero-crossing point and the slope, as well as the curve of growth for the integral (previously derived by Sánchez Almeidaet al., 1989, through the same approach), are reproduced quite well with a single atmosphere which assumes such simultaneous variations.The depth dependence of the fields that give the best fit in our model presents several striking properties which cannot be released without totally compromising the goodness of the fit. Namely, the magnetic field strength increases towards the observer while the downflowing velocity field decreases. Both variations must occur co-spatially, in the same atmospheric layers. This fact seems to contradict theoretical models for the fanning out parts of magnetic concentrations which foresee a sharp separation between a static magnetic layer and a deep zone with velocity fields. We discuss a possible solution of such contradiction in terms of a finite optical thickness of the boundary layer between zones with and without magnetic field in faculae.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Putative Meteoritic Craters in Río Cuarto (Central Argentina) Interpreted as Eolian Structures

Ten oblong aligned depressions in the Río Cuarto area (provincia de Córdoba, Argentina) were supposed to be the result of very-low-angle Holocene meteoroid impacts. However, we consider that authors that studied the structures did not demonstrated their extraterrestrial origin. We suggest that an eolian origin for the structures of Río Cuarto is more likely. Actually, these landforms integrate large systems of similar deflation/accumulation geoforms aligned according to predominant winds during different periods.     

On the use of logistic regression for stellar classification

We are totally immersed in the Big Data era and reliable algorithms and methods for data classification are instrumental for astronomical research. Random Forest and Support Vector Machines algorithms have become popular over the last few years and they are widely used for different stellar classification problems. In this article, we explore an alternative supervised classification method scarcely exploited in astronomy, Logistic Regression, that has been applied successfully in other scientific areas, particularly biostatistics. We have applied this method in order to derive membership probabilities for potential T Tauri star candidates from ultraviolet-infrared colour-colour diagrams.     

Isotropic and anisotropic pointing models

This paper describes an alternative approach for generating pointing models for telescopes equipped with serial kinematics, esp. equatorial or alt-az mounts. Our model construction does not exploit any assumption for the underlying physical constraints of the mount, however, one can assign various effects to the respective components of the equations. In order to recover the pointing model parameters, classical linear least squares fitting procedures can be applied. This parameterization also lacks any kind of parametric singularity. We demonstrate the efficiency of this type of model on real measurements with meter-class telescopes where the results provide a root mean square accuracy of 1.5?2 arcseconds.