Archive for September 2007

Water Clouds

xantox, 17 September 2007 in Gallery

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Terrestrial clouds are the result of extraordinarily complex interactions between water and air, with several feedback mechanisms combining the effects of fluid dynamics and thermodynamics.1

© 2004 Sarah Robinson & Jean Hertzberg, University of Colorado
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The kind of convective clouds known as cumulus are produced by the vertical winds occurring in regions of warm moist air, per Archimedes principle. This rapid lifting results in adiabatic expansion and cooling, and consequent accretion of water droplets. The irregular distribution of droplets scatters sunlight geometrically in all directions, producing a bright white appearance like in snow, decaying into gray shades as per their optical thickness. Each cloud is short-lived, lasting approximately 15 minutes in average.


  1. H. R. Pruppacher, J. D. Klett, “Microphysics of clouds and precipitation“, Springer (1997); R. A. Houze, “Cloud Dynamics“, Academic Press (1994) []
  2. © 2004 Sarah Robinson, Flow Visualization Course, University of Colorado []
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Genomes inside genomes

xantox, 5 September 2007 in News

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Scientists at the University of Rochester and the J. Craig Venter Institute have discovered a copy of the entire genome of Wolbachia, a bacterial parasite, residing inside the genome of its completely different host species Drosophila Ananassae, the fruitfly. To isolate the fly’s genome from the parasite’s, the flies were fed with a simple antibiotic, killing the Wolbachia, but Wolbachia genes were still there. The scientists found that the genes were residing directly inside the second chromosome of the insect, and that some of these genes are even transcribed in uninfected flies, so that copies of the gene sequence are made in cells that could be used to make Wolbachia proteins.

© University of Rochester

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