The chemistry of comets An annotated bibliography

Annotated bibliography on chemistry of comets - free radicals, photochemistry, photolysis, and spectral analysi

Error correction and diversity analysis of population mixtures determined by NGS

The impetus for this work was the need to analyse nucleotide diversity in a viral mix taken from honeybees. The paper has two findings. First, a method for correction of next generation sequencing error in the distribution of nucleotides at a site is developed. Second, a package of methods for assessment of nucleotide diversity is assembled. The error correction method is statistically based and works at the level of the nucleotide distribution rather than the level of individual nucleotides. The method relies on an error model and a sample of known viral genotypes that is used for model calibration. A compendium of existing and new diversity analysis tools is also presented, allowing hypotheses about diversity and mean diversity to be tested and associated confidence intervals to be calculated. The methods are illustrated using honeybee viral samples. Software in both Excel and Matlab and a guide are available at http://www2.warwick.ac.uk/fac/sci/systemsbiology/research/software/,the Warwick University Systems Biology Centre software download site.Publisher PDFPeer reviewe

The Magellanic Bridge cluster NGC 796: Deep optical AO imaging reveals the stellar content and initial mass function of a massive open cluster

NGC 796 is a massive young cluster located 59 kpc from us in the diffuse intergalactic medium of the 1/5-1/10 $Z_{\odot}$ Magellanic Bridge, allowing to probe variations in star formation and stellar evolution processes as a function of metallicity in a resolved fashion, providing a link between resolved studies of nearby solar-metallicity and unresolved distant metal-poor clusters located in high-redshift galaxies. In this paper, we present adaptive optics $gri$H$\alpha$ imaging of NGC 796 (at 0.5", which is ~0.14 pc at the cluster distance) along with optical spectroscopy of two bright members to quantify the cluster properties. Our aim is to explore if star formation and stellar evolution varies as a function of metallicity by comparing the properties of NGC 796 to higher metallicity clusters. We find from isochronal fitting of the cluster main sequence in the colour-magnitude diagram an age of 20$^{+12}_{-5}$ Myr. Based on the cluster luminosity function, we derive a top-heavy stellar initial mass function (IMF) with a slope $\alpha$ = 1.99$\pm$0.2, hinting at an metallicity and/or environmental dependence of the IMF which may lead to a top-heavy IMF in the early Universe. Study of the H$\alpha$ emission line stars reveals that Classical Be stars constitute a higher fraction of the total B-type stars when compared with similar clusters at greater metallicity, providing some support to the chemically homogeneous theory of stellar evolution. Overall, NGC 796 has a total estimated mass of 990$\pm200$ $M_{\odot}$, and a core radius of 1.4$\pm$0.3 pc which classifies it as a massive young open cluster, unique in the diffuse interstellar medium of the Magellanic Bridge.Comment: Accepted for publication in the Astrophysical Journal. Contains 14 pages, 11 figures, and 3 table

Millstone Hill Thomson Scatter Results for 1966

This report presents F-region electron densities and electron temperatures observed during the year 1966 at the Millstone Hill Radar Observatory (42.6°N, 71.5°W) by the UHF Thomson (incoherent) scatter radar. The measurements were usually made for periods of 24 hours twice per month, and covered the altitude range 150 to 750 km approximately. The time required to collect all the measurements spanning this height interval was 30 minutes, i.e., half that of previous years. The results exhibit a greater amount of random time variation than seen heretofore, partly as a result of the better time resolution achieved and partly because each day has been analyzed individually, i.e., we have discontinued the practice of computing only the monthly mean behavior. We believe, however, that the largest part of the random variation is real and results from fluctuations in the solar EUV flux, which increase in magnitude as the sunspot number rises. Also, we expect a growing incidence of fluctuations produced by large-scale traveling ionospheric disturbances as we approach sunspot maximum. Despite this variability, the characteristics “winter” and “summer” type behavior reported for Millstone in previous years is clearly recognizable. On four days in which pronounced effects due to geomagnetic storms are evident, the layer rose to great heights in the late afternoon and achieved an abnormally high density (and lower-than-normal temperature). The reverse behavior was encountered the next morning. This sequence is similar to that first seen in June 1965, and its interpretation in terms of current ideas is summarized

Millstone Hill Thomson Scatter Results for 1965

This report presents F-region electron densities, and electron and ion temperatures observed during the year 1965 at the Millstone Hill Radar Observatory (42.6°N. 71.5“W) by the UHF Thomson (incoherent) scatter radar. The measurements were made over 48-hour periods that were usually scheduled to include the International Geophysical World days near the center of each month. Geomagnetic storm sudden commencements occurred during two of the observing periods, but do not appear to have given rise to marked variation of the densities or temperatures. On the other band, measurements made during the progress of a major storm (15-19 June 1965) exhibit large changes compared with the behavior observed in the following month. The remaining months were magnetically quiet, and the density and temperature behavior were similar to those observed in 1964. Millstone is a midlatitude station exhibiting a characteristic “winter” and "summer” daytime density variation. The transition between these two types occurs rapidly around equinox, without any corresponding seasonal change in the F-region thermal structure. Current ideas concerning the mechanisms responsible for this and other features of diurnal and seasonal variations arc discussed