No abstract

We present a comprehensive catalog of ultraviolet (HST /STIS and FUSE ) absorbers in the lowredshift IGM at z < 0.4. The catalog draws from the extensive literature on IGM absorption, and it reconciles discrepancies among previous catalogs through a critical evaluation of all reported absorption features in light of new HST /COS data. We report on 746 H I absorbers down to a rest-frame equivalent width of 12 mÅ over a maximum redshift path length ∆z = 5.38. We also confirm 111 O VI absorbers, 29 C IV absorbers, and numerous absorption features due to other metal ions. We characterize the distribution of absorber line frequency as a function of column density as a power law, dN /dz ∝ N −β , where β = 2.08 ± 0.12 for O VI and β = 1.68 ± 0.03 for H I. Utilizing a more sophisticated accounting technique than past work, the catalog accounts for ∼ 43% of the baryons: 24 ± 2% in the photoionized Lyα forest and 19 ± 2% in the WHIM as traced by O VI. We discuss the large systematic effects of various assumed metallicities and ionization states on these calculations, and we implement recent simulation results in our estimates.

We have used archival FUSE data to complete a survey of interstellar HD in 41 lines of sight with a wide range of extinctions. This follow-up to an earlier survey was made to further assess the utility of HD as a cosmological probe; to analyze the HD formation process; and to see what trends with other interstellar properties were present in the data. We employed the curve-of-growth method, supported by line profile fitting, to derive accurate column densities of HD. We find that the N(HD)/2N(H 2 ) ratio is substantially lower than the atomic D/H ratio and conclude that the molecular ratio has no bearing on cosmology, because local processes are responsible for the formation of HD. Based on correlations with E(B À V ), H 2 , CO, and iron depletion, we find that HD is formed in the densest portion of the clouds; the slope of the log N (HD)/log N (H 2 ) correlation is greater than 1.0, caused by the destruction rate of HD declining more slowly than that of H 2 ; and, as a sidelight, that the depletions are density dependent.

Activated mononucleotides oligomerize in the presence of montmorillonite clay to form RNA oligomers. In the present study, effects of salts, temperature and pH on the clay-catalyzed synthesis of RNA oligomers were investigated. This reaction is favored by relatively high concentration of salts, such as 1 M NaCl. It was shown that the presence of divalent cations was not required for this reaction. High concentrations of NH4+ and HCO3- and 0.01 M HPO4(2-) inhibit the reaction. The yields of RNA oligomers decreased as the temperature was raised from 4 degrees C to 50 degrees C. A5' ppA was the major product at pH's below 6. The catalytic activity of a variety of minerals and three meteorites were investigated but none of them except galena catalyzed the oligomerization. ATP was generated from ADP but it was due to the presence of HEPES buffer and not due to the minerals. Meteorites catalyzed the hydrolysis of the pyrophosphate bonds of ATP. The results suggest that oligomers of RNA could have formed in pH 7-9 solutions of alkali metal salts in the presence of montmorillonite clay.