The DNA de-methylating agent 5-azacytidine does not restore CYP1A induction in PCB resistant Newark Bay killifish (Fundulus heteroclitus)

Newark Bay (NB) killifish (Fundulus heteroclitus) have been chronically exposed to environmental contaminants that activate the aryl hydrocarbon receptor (AHR) and are tolerant to toxic effects and CYP1A induction provoked by AHR ligands. Resistance to CYP1A induction could be due to an epigenetic mechanism such as DNA methylation. We measured in-ovo CYP1A catalytic activity (ethoxyresorufin-O-deethylase, EROD) in NB and reference site killifish embryos aqueously exposed to various concentrations of the de-methylating agent 5-azacytidine, 5-AC (5, 50 and 500 μ(micro)M) with or without 0.2 μ(micro)g/l of the CYP1A inducer 3,3^′,4,4^′,5 pentachlorobiphenyl (IUPAC PCB126). Neither PCB126 alone, nor PCB126 plus 5-AC, induced EROD above levels in vehicle treated Newark Bay fish. In reference site fish, the same PCB126 dose provoked a 7.4-fold EROD induction relative to controls. We conclude that Newark Bay killifish are resistant to CYP1A induction by co-planar PCBs during early embryological development and our data suggests that DNA methylation does not play a critical role in resistance to CYP1A induction in this model.     

Numerical models of mantle convection with secular cooling

A 2-D time-dependent finite-difference numerical model is used to investigate the thermal character and evolution of a convecting layer which is cooling as it convects. Two basic cooling modes are considered: in the first, both upper and lower boundaries are cooled at the same rate, while maintaining the same temperature difference across the layer; in the second, the lower boundary temperature decreases with time while the upper boundary temperature is fixed at 0°C. The first cooling mode simulates the effects of internal heating while the second simulates planetary cooling as mantle convection extracts heat from, and thereby cools, the Earth's core. The mathematical analogue between the effects of cooling and internal heating is verified for finite-amplitude convection. It is found that after an initial transient period the central core of a steady but vigorous convection cell cools at a constant rate which is governed by the rate of cooling of the boundaries and the viscosity structure of the layer. For upper-mantle models the transient stage lasts for about 30 per cent of the age of the Earth, while for the whole mantle it lasts for longer than the age of the Earth. Consequently, in our models the bulk cooling of the mantle lags behind the cooling of the core-mantle boundary. Models with temperature-dependent viscosity are found to cool in the same manner as models with depth-dependent viscosity; the rate of cooling is controlled primarily by the horizontally averaged variation of viscosity with depth. If the Earth's mantle cools in a similar fashion, secular cooling of the planet may be insensitive to lateral variations of viscosity.     

Rain infiltration and crust formation in the extreme arid zone of the Atacama Desert, Chile

A key question in understanding life on Mars under dry(ing) conditions is how arid soils respond to small levels of liquid water. We have conducted a series of simulated rain experiments in the hyperarid core region of the Atacama Desert. Rain amounts from 0.24 to 3.55 mm were applied in the early evening to the soil. We conclude that rain events of less than 1 mm do not saturate the surface, and the soil humidity at the surface remains below 100%. Rain events of 2 mm or more generate free water in the pore space of the soil surface, which may be necessary to support biological activity in the soil. The crust on the surface of the soil is a strong barrier to the diffusion of subsurface moisture and subsequent evaporation. Our results show that once the relative humidity in hyperarid soils begins to fall below 100% the rate of decrease is quite rapid. Thus, the precise value assumed for the limits of life or water activity, do not appreciably change the time of water availability resulting from small desert rains. The Atacama Desert results may be applied to models of (H₂O) wetting in the upper soils of Mars due to light rains, melting snow and heavy precipitating fog.     

Influence of frothers on floatability. II. Flotation of chalcocite and quartz mixtures

Influence of frothers (α-terpineol or n-amyl alcohol) on the floatability of chalcocite and quartz mixtures, with potassium ethyl xanthate as a collector at pH 5.5–6, was investigated with a Hallimond tube.Activation of quartz by the presence of chalcocite was observed and interpreted as due to copper ionic species originating from chalcocite oxidation products. Best selectivity of separation between chalcocite and quartz was obtained when the frother concentration was kept sufficiently low. Collector—frother interactions during formation of three-phase mineral grain/solution/gas bubble contacts were observed.     

Unified structural classification of AB2 molecules and solids from valence electron orbital radii

We present structural plots for AB₂ molecules and solids with sp-bonding based on parameters derived from valence electron orbital radii. We show that the same schemes that allow one to classify crystals with different structures, are also able to distinguish molecular shapes into linear and bent. Our picture is consistent with the existence of a critical numberN _c =16of valence electrons, in agreement with the Mulliken-Walsh rule, and accounts for many exceptions to the latter in the caseN≤16. We discuss critically our findings and announce new results on AB₃ molecules. We also discuss preliminary results of model calculations on AB₂ molecules.     

Three-Dimensional Modeling of Shallow Shear-Wave Velocities for Las Vegas, Nevada, Using Sediment Type

A three-dimensional model of near-surface shear-wave velocity in the deep alluvial basin underlying the metropolitan area of Las Vegas, Nevada (USA), is being developed for earthquake site response projections. The velocity dataset, which includes 230 measurements, is interpolated across the model using depth-dependent correlations of velocity with sediment type. The sediment-type database contains more than 1 400 well and borehole logs. Sediment sequences reported in logs are assigned to one of four units. A characteristic shear-wave velocity profile b developed for each unit by analyzing closely spaced pairs of velocity profiles and well or borehole logs. The resulting velocity model exhibits reasonable values and patterns, although it does not explicitly honor the measured shear-wave velocity profiles. Site response investigations that applied a preliminary version of the velocity model support a two-zone ground-shaking hazard model for the valley. Areas in which clay predominates in the upper 30 m are predicted to have stronger ground motions than the rest of the basin.     

Constraining the 13C neutron source in AGB stars through isotopic analysis of trace elements in presolar SiC

Abstract— Analyses of the isotopic compositions of multiple elements (Mo, Zr, and Ba) in individual mainstream presolar SiC grains were done by resonant ionization mass spectrometry (RIMS). While most heavy element compositions were consistent with model predictions for the slow neutron capture process (s‐process) in low‐mass (1.5–3 M_⊙) asymptotic giant branch stars of solar metallicity when viewed on single‐element three‐isotope plots, grains with compositions deviating from model predictions were identified on multi‐element plots. These grains have compositions that cannot result from any neutron capture process but can be explained by contamination in some elements with solar system material. Previous work in which only one heavy element per grain was examined has been unable to identify contaminated grains. The multi‐element analyses of this study detected contaminated grains which were subsequently eliminated from consideration. The uncontaminated grains form a data set with a greatly reduced spread on the three‐isotope plots of each element measured, corresponding to a smaller range of ¹³C pocket efficiencies in parent AGB stars. Furthermore, due to this reduced spread, the nature of the stellar starting material, previously interpreted as having solar isotopic composition, is uncertain. The constraint on ¹³C pocket efficiencies in parent stars of these grains may help uncover the mechanism responsible for formation of ¹³C, the primary neutron source for s‐process nucleosynthesis in low‐mass stars.     

The influence of surface oxidation of chalcocite on its floatability and ethyl xanthate sorption

The results obtained from measurements of potassium ethyl xanthate (EtXK) sorption by synthetic chalcocite (Cu₂S) and the results of chalcocite floatability measurements are presented.Five chalcocite samples, denoted as Cu₂S A, B, C, D and E, were used for the measurements. Chalcocite samples of 60–75 μm were prepared in the same manner but were kept under conditions which differed in their degree to prevent surface oxidation by atmospheric oxygen.Chalcocite surface oxidation has a strong effect both on xanthate sorption and on chalcocite floatability. The maximal amount of xanthate abstracted (Q_max) by chalcocite samples from deoxygenated solutions after a long sorption period increases with increasing oxidation of the samples. The Q_max values give information concerning the total amount of surface oxidation products.Chalcocite decreases its floatability with increasing surface oxidation. Most oxidized chalcocite samples required an about 100 times greater collector consumption to obtain the same flotation results than the least-oxidized samples studied.     

Influence of frothers on floatability. I. Flotation of single minerals (quartz and synthetic chalcocite)

The flotation and sorption properties of chalcocite and quartz in potassium ethyl xanthate (EtXK), frothers (α-terpineol and n-amyl alcohol), and (xanthate + frother) mixed solutions were investigated. Surface tension and frothing properties of the solutions were also measured.Floatability and sorption properties of the minerals investigated strongly depended on any controlled or uncontrolled change occurring at the mineral surface. Surface oxidation of chalcocite was shown to be an especially important parameter.The frothers studied showed some collecting properties in respect to chalcocite and quartz and influenced the xanthate sorption on chalcocite.Comparison of the flotation recoveries in frother solutions respectively with and without xanthate indicated an occurrence of noticeable collector-frother interactions during formation of the bubble/chalcocite grain aggregate. No such interactions were found for quartz.Influence of the frothers on floatability of the minerals was observed at different frother concentrations but at close values of surface pressure (π) and of retention time (rt).