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  • 1
    Publication Date: 2004-10-05
    Description: We use several independent constraints on the number of ecliptic comets to estimate impact cratering rates on the Jupiter moons. The impact rate on Jupiter by 1.5-km diameter ecliptic comets is currently NY(d 〉 1.5km) = 0.005(+0.006)(-0.003) per annum. Asteroids and long period comets are currently unimportant. The size-number distribution of ecliptic comets smaller than 20 km is inferred from size-number distributions of impact craters on Europa, Ganymede, and Triton. For comets bigger than 50 km we use the size-number distribution of Kuiper Belt Objects. The overview of the impact rate at Jupiter in general and at Europa in particular are given. These impact rates imply cratering rates on Europa of 0.5 per Ma per 10(exp 6) sq km for impact craters bigger than 1 km, and of 0.015 per Ma per 10(exp 6) sq km for impact craters bigger than 20 km. The latter corresponds to an average recurrence time of 2.2 Ma for 20 km craters. The best current estimates for the number of 20 km craters on Europa appear to range between about twelve to thirty. This implies that the average age of Europa's surface is between 30 and 70 Ma. The average density of craters with diameter greater than 1 km on well-mapped swaths on Europa is 30 per 10(exp 6) sq km. The corresponding nominal surface age would be 60 Ma. These two estimates are not truly independent because we have used size-number distribution of the Europan craters to help generate the size-number distribution of comets. The uncertainty of the best estimate - call it 42 Ma for specificity - is at least a factor of 3.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Workshop on Europa's Icy Shell: Past, Present, and Future; 98-99; LPI-Contrib-1195
    Format: text
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 6 (1992), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The gene, flaA, encoding the flagellin protein of Listeria monocytogenes (strain 12067) has been isolated from an expression library in Escherichia coli using a flagellin-specific monoclonal antibody. DNA sequence analysis of a positive clone revealed the presence of an open reading frame of 287 amino acid residues with a calculated molecular mass of 30.4 kDa. Comparison of this sequence with flagellins from other bacteria showed a significant degree of homology in both the N- and C-terminal parts of the protein. The flagellin mRNA was determined to be 1 kb in size, which is the expected size for a monocistronic mRNA, and the temperature-dependent expression of flagellin was found to be regulated at the transcriptional level. Southern blot analysis, using the flagellin gene as probe, indicated that L. monocytogenes can be divided into two groups. These groups correspond to the flagellar antigens AB and ABC, respectively, as well as to the two types of L. monocytogenes based on the DNA sequence of the listeriolysin gene.
    Type of Medium: Electronic Resource
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