Ecotoxicological evaluation of polycyclic aromatic hydrocarbons using marine invertebrate embryo–larval bioassays

The toxicity of polycyclic aromatic hydrocarbons (PAHs) was determined using mussel, sea-urchin and ascidian embryo–larval bioassays. Fluorescent light exposure enhanced phenanthrene, fluoranthene, pyrene and hydroxypyrene toxicity in comparison with dark conditions, but not naphthalene and fluorene toxicity. The toxicity of PAHs was inversely related to their K_OW values following QSAR models derived for baseline toxicity of general narcotics, whereas the obtained regression using toxicity data from photoactivated PAHs significantly departed from the general narcosis model. Also, the mixture toxicity of five PAHs to the larval growth of the sea-urchin was compared with predictions derived from the concentration addition concept, indicating less than additive effects. Finally, we compared our toxicity data with worst-case environmental concentrations in order to provide a preliminary estimate of the risk to the marine environment. Naphthalene, fluorene and pyrene are not considered to pose a risk to sea-urchin, mussel or ascidian larvae, whilst phenanthrene and fluoranthene may pose a risk for mussel and sea-urchin. Moreover, a higher risk for those species is expected when we consider the photoactivation of the PAHs.     

Characteristics of microscale evapotranspiration: a comparative analysis

Summary ?Evapotranspiration characteristics on the point-scale (several hundred square meters) and the local scale (several square kilometers) are analysed by comparing a deterministic and a statistical – deterministic surface energy balance model. The vegetation surface variability is represented by both the surface heterogeneity and inhomogeneity. Heterogeneity means the mosaic of wet (wif ≠ 0) and dry (1-wif) fractions of vegetation surface, while inhomogeneity addresses small scale variations of soil moisture content. The microscale characteristics of evapotranspiration are considered in terms of analysing evapotranspiration E _v versus soil moisture content θ, relative frequency distribution characteristics of E _v (θ) and the aggregation algorithms for its estimation. The analyses are performed for loam soil type under different atmospheric forcing conditions. The main result is as follows: For dry vegetation surface (wif = 0), the relationship between the aggregated (θ_agg) and the area-averaged (θ _m ) soil moisture content is nonlinear and depends on both the states of the surface and the atmospheric forcing conditions. In the study, we assumed that there are no advective effects and mesoscale circulation patterns induced by surface discontinuities. Based on this fact it seems unlikely to be able to construct an aggregation algorithm for calculating θ_agg without inclusion of the atmospheric forcing conditions. This means that it will be difficult to construct a simple formula for calculating area-averaged transpiration, if it is possible at all. Received May 3, 2001; revised May 31, 2002; accepted June 3, 2002     

A sedimentary facies model for stepped,fluvial tufa systems in the Iberian Range (Spain): the Quaternary Piedra and Mesa valleys

Stratigraphic and sedimentological analyses of the Quaternary tufa and associated deposits in the Piedra and Mesa river valleys allowed a number of stages of their sedimentary evolution to be characterized, and a depositional sedimentary model for this north‐central sector of the Iberian Range (Spain) to be established. The proposed sedimentary facies model may explain tufa arrangements in other medium to high gradient, stepped, fluvial tufa systems with narrow transverse profiles occurring in temperate, semi‐arid areas, in both recent and past scenarios. There are several tufa deposits within the Piedra and Mesa river valleys that, over a maximum thickness of about 90 m, record one or more stages of tufa deposition produced following the fluvial incision of the bedrock or previous tufa deposits. Each depositional stage begins with coarse detrital sedimentation. Six fundamental, vertical sequences of tufa facies with small amounts of detrital material reveal the sedimentary processes that occurred in different fluvial environments: channel areas with: (i) free‐flowing water; (ii) barrages and/or cascades; and (iii) dammed water and palustrine floodplains. The proposed sedimentary model involves narrow, stepped, fluvial valleys in which tufa cascades were common. Alternating intervals of bryophyte and stromatolite facies commonly formed at some cascades. Many of these represented barrage‐cascade structures that consisted of phytoclast rudstones, thick phytoherms of mosses and associated stromatolites, and curtain‐shaped phytoherms of stems. Upstream of these structures, dammed areas with bioclastic sands and silts developed and palustrine vegetation grew. The channel stretches between barrages and/or cascades were loci for extensive stromatolite growth in fast flowing water. The palustrine floodplain was home to pools and drainage channels. The model also explains the growth of some barrages in the River Piedra that surpassed the height of the divide, with the diffluence of the main channel into a secondary course forming other tufa deposits in the area. The distribution and abundance of certain types of tufa facies in fluvial basins may be an indicator of differences in their gradients. The facies studied in this work suggest that the gradient of the ancient River Piedra was steeper than that of the ancient River Mesa. Assuming similar scenarios for climate and hydrology, the depositional settings mentioned above and their dimensions would have been determined mainly by the gradient and width of the associated river valleys. This sedimentary model may also be useful for inferring variations in other river basin slopes, as well as accounting for the presence of tufas in areas that normally have no permanent water input.     

Dynamic fuzzy neural network for simulating the fixed-bed adsorption of cadmium,nickel, and zinc on bone char

This study introduces the application of a dynamic fuzzy neural network for fitting and simulating the adsorption of nickel, cadmium, and zinc ions in mono- and bi-metallic solutions (nickel–cadmium, nickel–zinc, and cadmium–zinc) using packed-bed columns with bone char. This neural network model has shown a flexible and self-adaptive architecture with a faster learning speed than that of traditional artificial neural approaches. Results showed that this neural network model was reliable for representing the high asymmetry behavior of concentration profiles in both mono- and bi-metallic breakthrough curves where its accuracy was quite reasonable. Breakthrough parameters for mono-component and binary systems of tested heavy metals were calculated and compared. This analysis showed that the removal of these heavy metal ions in binary systems was a strong competitive adsorption process where the presence of co-ions reduced the removal performance of bone char at fixed-bed adsorbers. Results of surface characterization of adsorbent samples with X-ray photoelectron and infrared spectroscopy supported a removal mechanism based on an ion exchange between calcium from hydroxyapatite of bone char and heavy metal ions in the solution forming new metal–phosphate interactions in the adsorbent surface.     

An effective Lagrangian description of supernova-core bounce

In standard hydrodynamical supernova computations many variables are needed to describe the time evolution of the stellar core. A numerical grid of points is usually constructed to attain the desirable accuracy. This fact limits the codes to run in the biggest and fastest computers. A new semi-analytical approach for the problem of the dynamical evolution of the collapse, bounce and explosion of a supernova core is proposed. The relevant coordinates of the dynamical problem are chosen to define an effective Lagrangian. The Lagrangian variables are the radii of the shells, seen now as collective coordinates, which describe the global aspects of the process. An effective Lagrangian with these properties for any number of shells is presented. The equations of motion are obtained from this Lagrangian and then integrated numerically. The potentiality of the method is exemplified for the extreme case in which only two shells are used to describe the stellar core. Even in this instance, it is possible to discuss the circumstances for the occurrence of supernova explosion.     

Women in the History of Astronomy

We think about the History of Astronomy as the History of men. As the History of a few men: Ptolemy, Copernicus, Kepler, Newton,...- men who have changed our way of looking at the sky. But the History of Astronomy is more than that, it is the History of thousand of people whose daily work has allowed the development of knowledge and scientific theories at the time they lived. This, sometimes, "tedious work" permitted the big steps. Many of these people were women, as Theano who married Pythagoras and taught mathematics and astronomy in his school, Hypatia who managed the Library of Alexandria and wrote several astronomical treatises, Hildegard of Bingen who developed a theory on the origin and structure of the Universe in the 12^th century, or Sofie Brahe who, worked with her famous brother. And so many privileged women who after a long process of study, were able to develop their scientific interests in spite of been excluded from most of the educational installations and formal and informal groups of men scientist. Most of the works done by these women have been ignored, or wrongly attributed to men throughout History. It often happens that although they have been recognized as good scientists in their own times, women have been discredited by posterior historians who refused to believe that important women scientist ever existed. Here we intend to make a short summary on the lives of some of these women and their astronomical works. This revised version was published online in July 2006 with corrections to the Cover Date.     

Chemical Evolution in the Early Universe: Can Damp Lyα Systems Be Spiral Galaxies?

The distribution of element abundances with redshift in Damped Lyα (DLA) systems can be adequately reproduced by the same models reproducing the halo and disk components of the Milky Way Galaxy at different galactocentric distances. In this sense, DLA systems are well represented by normal spiral galaxies in their early evolutionary stages. This revised version was published online in July 2006 with corrections to the Cover Date.     

A New Method to Determine the Derivatives of the Laplace Coefficients

The determination of the secular variations of the orbital elements of objects in N-body systems is based on the literal development of the perturbing function. The development makes use of the Laplace coefficients and their derivatives. In this paper a new method is described for the analytical computation of the derivatives of the Laplace coefficients. It is an explicit formula in the sense that it only contains the Laplace coefficients and the parameter on which the Laplace coefficients depend. The advantage of this method is that it is unnecessary to calculate all the derivatives up to the desired order. It is enough to calculate the Laplace coefficients. Easy coding is a further benefit of the method and it provides more accurate numerical results. The paper describes in detail the application of the method through an example and gives comparison with former methods.This revised version was published online in October 2005 with corrections to the Cover Date.