1,3-Butadiene (butadiene) is a potent carcinogen in mice, but not in rats. Metabolic studies may provide an explanation of these species differences and their relevance to humans. Male Sprague-Dawley rats and B6C3F1 mice were exposed for 6 h to 200 ppm [2,3-14C]-butadiene (specific radioactivity [sa] 20 mCi/mmol) in a Cannon nose-only system. Radioactivity in urine, feces, exhaled volatiles and 14C-CO2 were measured during and up to 42 h after exposure. The total uptake of butadiene by rats and mice under these experimental conditions was 0.19 and 0.38 mmol (equivalent to 3.8 and 7.5 mCi) per kg body weight, respectively. In the rat, 40% of the recovered radioactivity was exhaled as 14C-CO2, 70% of which was trapped during the 6-h exposure period. In contrast, only 6% was exhaled as 14C-CO2 by mice, 3% during the 6-h exposure and 97% in the 42 h following cessation of exposure. The formation of 14C-CO2 from [2,3-14C]-labeled butadiene indicated a ready biodegradability of butadiene. Radioactivity excreted in urine accounted for 42% of the recovered radioactivity from rats and 71% from mice. Small amounts of radioactivity were recovered in feces, exhaled volatiles and carcasses. Although there was a large measure of commonality, the exposure to butadiene also led to the formation of different metabolites in rats and mice. These metabolites were not found after administration of [4-14C]-1,2-epoxy-3-butene to animals by i.p. injection. The results show that the species differences in the metabolism of butadiene are not simply confined to the quantitative formation of epoxides, but also reflect a species-dependent selection of metabolic pathways. No metabolites other than those formed via an epoxide intermediate were identified in the urine of rats or mice after exposure to 14C-butadiene. These findings may have relevance for the prediction of butadiene toxicity and provide a basis for a revision of the existing physiologically based pharmacokinetic models.
Specimens from the meteorite fall at 1:05 a. m., on 8 February 1969 at Pueblito de Allende, Chihuahua, Mexico, have been recovered. The meteorite is a chondrite (C3 and C4) with both opaque and microcrystalline matrices. Specimens were brought to a low background gamma counter less than 4 (1/2) days after the fall, and gamma rays from short-lived isotopes have been observed.
Nine polishled thin sectionis have been exposed to nulclear track plates, three have been counted by alplia-particle spectrometry, and one has been examined by electron mocroprobe. Interpretation of the results is in a preliminary stage. Alpha track distribiutioni in the autoradiograph of a breccia forms a network that appears related to the rims of accretionary lapilli comiiposinig the breccia. Thorium in a coarse-grained crystalline rock is concenitrated in micron-sized, zirconium-rich crystals. Alplia count rates agree with what would be predicted from previously reported thorium and uranium contents of the same rocks, suggesting secular equilibriunm for the thorium and uranium decay series.
Twenty-nine samples of bauxites from different locations were analyzed for Th and U by gamma-ray spectrometric, alpha counting, and wet chemical methods. The Th concentrations range from 5.0 to 131 p.p.m. and average 48.9 p.p.m. The U concentrations range from 2.7 to 26.7 p.p.m. and average 11.4 p.p.m. The Th-to-U ratios range from 1.5 to 20.9, with an average value of 5.1. Zr determinations on some of the bauxites gave values ranging from 0.02 to 0.65% Zr, and averaging 0.09% Zr. The Th, U, and Zr contents of the bauxites are related to the type of source rock. Bauxites derived from nepheline syenites contain more Th and U than bauxites derived from other rock types; bauxites derived from basic igneous rocks have the lowest Th and U concentrations, and bauxites derived from carbonate rocks have the lowest Th-to-U ratios. The greatest concentrations of Zr were found in bauxites derived from nepheline syenites, and bauxites derived from carbonates contained the lowest concentrations of Zr. A study of samples from alumina plants treating Surinam and Arkansas bauxites shows that during the process, over 70% of the Th and U in these 2 bauxites is concentrated into the red mud, and the alumina contains very small amounts of these elements. This study also indicated that much of the Th and U in bauxites occurs in either primary or secondary resistate minerals.
Determining the hydraulic conditions whereby gravel dunes first develop in subaqueous environments is fundamental as their presence may influence engineering solutions designed to maintain bed stability. In addition, estimates of the flow conditions associated with preserved gravel bed forms in sedimentary sequences are useful for reconstructing the depositional environments and geometries of, for example, oil‐ and gas‐bearing geological strata. Consequently, a series of experiments considered dune initiation. In these experiments, defects and latterly incipient dunes developed from lower‐stage plane gravel beds during near‐threshold conditions of motion (θ/θ crit = 1.0–1.016) and long periods of marginal bed load transport rates. The three‐dimensional defects were almost imperceptible positive ovoid features with heights of one or two grain diameters and lengths and spans of a few decimeters. After 17 hours of flow, incipient, low‐amplitude, simple two‐dimensional dunes developed from the defects, with heights ranging between 0.029 and 0.055 m, nonequilibrium wavelengths of 1–4 m and spans of 0.6–0.9 m. Continued development over several days, with θ/θ crit ratios of around 1.3, resulted in near‐equilibrium two‐dimensional dunes with wavelengths averaging 2.6–3.5 m and spans equal to the flume width (4 m). The inception of incipient dunes could be predicted using bulk flow models; however, this approach was not suitable for the prediction of defect development. Near‐bed turbulence, in the form of small‐scale sweep events of limited breadth, controls the initiation of defects, but larger‐scale, coherent turbulent structures in the outer flow are related to dune development. Significantly, both defects and incipient dunes can exist at the same time, which indicates that the effects of sweeps on the bed morphology persist at the same time as larger‐scale turbulent structures are beginning to effect sediment transport.
The use of satellite data for the analysis of coastal and nearshore marine application in general, and urban waterfront land in particular, has been very limited due in most part to the lack of sufficient surface resolution. This project uses the new Landsat sensor the Thematic Mapper whose surface resolution is 30 meters, and also records three new bands of electromagnetic radiation. For the same area of coverage of Newport, RI, the TM classification identified twenty-one classes including both land and nearshore features and Multispectral Scanner classification identified eight classes. Use of the Thematic Mapper for urban waterfront classification shows significant improvement over the Multispectral Scanner.
Determining changes in the composition of cell populations is made possible by technologies like single-cell transcriptomics, CyTOF, and microbiome sequencing. However, existing methods for differential abundance do not model some ...Cellular omics such as single-cell genomics, proteomics, and microbiomics allow the characterization of tissue and microbial community composition, which can be compared between conditions to identify biological drivers. This strategy has been critical to ...
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