Browsing by Subject "ratio"
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Item The CN Isotopic Ratios In Comets(2009-08) Manfroid, J.; Jehin, E.; Hutsemekers, D.; Cochran, A.; Zucconi, J. M.; Arpigny, C.; Schulz, R.; Stuwe, J. A.; Ilyin, I.; Cochran, A.Our aim is to determine the isotopic ratios (12)C/(13)C and (14)N/(15)N in a variety of comets and link these measurements to the formation and evolution of the solar system. The (12)C/(13)C and (14)N/(15)N isotopic ratios are measured for the CN radical by means of high-resolution optical spectra of the R branch of the B-X (0, 0) violet band. 23 comets from different dynamical classes have been observed, sometimes at various heliocentric and nucleocentric distances, in order to estimate possible variations of the isotopic ratios in parent molecules. The (12)C/(13)C and (14)N/(15)N isotopic ratios in CN are remarkably constant (average values of, respectively, 91.0 +/- 3.6 and 147.8 +/- 5.7) within our measurement errors, for all comets whatever their origin or heliocentric distance. While the carbon isotopic ratio does agree with the terrestrial value (89), the nitrogen ratio is a factor of two lower than the terrestrial value (272), indicating a fractionation in the early solar system, or in the protosolar nebula, common to all the comets of our sample. This points towards a common origin of the comets independently of their birthplaces, and a relationship between HCN and CN.Item Influence of the Ratio Between the Translation and Contra-Rotating Coating Mechanism on Different Laser Sintering Materials and Their Packing Density(University of Texas at Austin, 2017) Meyer, L.; Wegner, A.; Witt, G.An initial study about the advanced machine parameters and their impact on the packing density of different laser sintering materials was conducted on a self-developed laser sintering machine. Usually, on commercial machines, the ratio between the translational and contra-rotatory movement of the roller is fixed. The standard ratio is established for polyamide 12, but new materials, such as polyamide 6 or polybutylene terephthalate, need adjustable parameters to find optimized composition coating results. In the testing machine, the contra rotating roller can be replaced by a coating blade to generate the powder layers. In Addition to the tests with the roller, two different shapes of coating blades were tested. This allows a comparison between both commercial coating systems in laser sintering machines.Item Large Excess of Heavy Nitrogen in Both Hydrogen Cyanide and Cyanogen from Comet 17P/Holmes(2008-05) Bockelee-Morvan, D.; Biver, N.; Jehin, E.; Cochran, Anita L.; Wiesemeyer, H.; Manfroid, J.; Hutsemekers, D.; Arpigny, C.; Boissier, J.; Cochran, W.; Colom, P.; Crovisier, J.; Milutinovic, N.; Moreno, R.; Prochaska, J. X.; Ramirez, I.; Schulz, R.; Zucconi, J. M.; Cochran, Anita L.; Cochran, W.From millimeter and optical observations of the Jupiter-family comet 17P/Holmes performed soon after its huge outburst of 2007 October 24, we derive N-14/N-15 = 139 +/- 26 in HCN and N-14/N-15 = 165 +/- 40 in CN, establishing that HCN has the same nonterrestrial isotopic composition as CN. The same conclusion is obtained for the long-period comet C/1995 O1 (Hale-Bopp) after a reanalysis of previously published measurements. These results are compatible with HCN being the prime parent of CN in cometary atmospheres. The N-15 excess relative to the Earth's atmospheric value indicates that N-bearing volatiles in the solar nebula underwent important N isotopic fractionation at some stage of solar system Formation. HCN molecules never isotopically equilibrated with the main nitrogen reservoir in the solar nebula before being incorporated in Oort Cloud and Kuiper Belt comets. The C-12/C-13 ratios in HCN and CN are measured to be consistent with the terrestrial value.Item A Study of Tests of Cylinders and Cores Taken From Convrete Roads in Texas During 1928(University of Texas at Austin, 1929-06-08) University of Texas at Austin