158 research outputs found
Type Ia Supernovae: Non-standard Candles of the Universe
We analyze the influence of the evolution of light absorption by gray dust in
the host galaxies of type Ia supernovae (SNe Ia) and the evolution of the mean
combined mass of close-binary carbon-oxygen white dwarfs merging due to
gravitational waves (SNe Ia precursors) on the interpretation of Hubble
diagrams for SNe Ia. A significant increase in the mean SNe Ia energy due to
the higher combined masses of merging dwarfs should be observable at redshifts
z > 2. The observed relation between the distance moduli and redshifts of SNe
Ia can be interpreted not only as evidence for accelerated expansion of the
Universe, but also as indicating time variations of the gray-dust absorption of
light from these supernovae in various types of host galaxies, observational
selection effects, and the decrease in mean combined masses of merging
degenerate dwarfs.Comment: 14 pages, 2 figure
Effects of metal-contaminated soils on the accumulation of heavy metals in gotu kola (Centella asiatica) and the potential health risks: a study in Peninsular Malaysia
Centella asiatica is a commonly used medicinal plant in Malaysia. As heavy metal accumulation in medicinal plants which are highly consumed by human is a serious issue, thus the assessment of heavy metals in C. asiatica is important for the safety of consumers. In this study, the heavy metal accumulation in C. asiatica and the potential health risks were investigated. Samples of C. asiatica and surface soils were collected from nine different sites around Peninsular Malaysia. The concentration of six heavy metals namely Cd, Cu, Ni, Fe, Pb and Zn were determined by air-acetylene flame atomic absorption spectrophotometer (AAS). The degree of anthropogenic influence was assessed by calculating the enrichment factor (EF) and index of geoaccumulation (Igeo). The heavy metal uptake into the plant was estimated through the calculation of translocation factor (TF), bioconcentration factor (BCF) and correlation study. Estimated daily intakes (EDI) and target hazard quotients (THQ) were used to determine the potential health risk of consuming C. asiatica. The results showed that the overall surface soil was polluted by Cd, Cu and Pb, while the uptake of Zn and Ni by the plants was high. The value of EDI and THQ showed that the potential of Pb toxicity in C. asiatica was high as well. As heavy metal accumulation was confirmed in C. asiatica, daily consumption of the plant derived from polluted sites in Malaysia was not recommended
Chemical characterization of cloud episodes at a ridge site in Tuscan Appennines, Italy
Cloudwater samples were collected from November 1992 to March 1995 in Vallombrosa, a mountain site of the Tuscan Apennines (central Italy). Chemical analyses show that all examined inorganic ions contributed significantly to the total ionic content (TIC). The ratio SO4/NO4 ranged from 0.92 to 3.46 and was > 1 for 86% of samples. There is a wide range in the chemical composition of the cloudwater. The total ionic content ranged from 640 to 7476 Aeq l 1 and pH from 3.17 to 6.22. The liquid water content (LWC) ranged from 0.06 to 0.94 g m 3 and electrical conductivity from 47 to 485 AV 1. The total ionic content decreases while the liquid water content increases. Also analyzed were soluble trace metals (Fe, Pb, Cu, Mn, Cd, Al), synthetic anionic surfactants and the methanesulphonic acid. Chemical analyses evidenced in some cases a high concentration of organic matter. The meteorological analysis for a few samples of individual passages was carried out for the possibility of establishing a correspondence between meteorological events and chemical composition. The sources (marine, crustal and anthropogenic) of chemical components were deduced
Variable influence of the atmospheric flux on the trace metal chemistry of oceanic suspended matter
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