Educação matemática pela arte
Gusmão, Lucimar Donizete
2013-08-28
Search results
191 records were found.
This paper reviews the developments of the 1980s in the characterisation of organically-bound sulphur in the geosphere and summarises the geochemical significance of the results obtained by these studies. The identification of more than 1500 novel OSC (organic sulphur compounds) with structures related to biochemical precursors in mostly immature sediments and crude oils has led to a better understanding of the process by which inorganic sulphur is incorporated into organic matter. The sulphur enrichment of organic matter probably takes place via 'quenching' of functionalised lipids by sulphur at the early stages of sediment diagenesis or even in the water column. This results in the formation of OSC with specific structures which may be applied as palaeoenvironmental indicators. Hydrocarbon biological marker distributions may be heavi...
Li et al. try to revive the condensation theory. Their attempts for condensation of phytol with phenols are unconvincing to us. Only one of the five tests of their hypothesis, a search for methylated MTTCs and their precursors in organisms, seems useful to us.
A critical review of literature concerning the molecular characterization of low and high molecular weight organosulphur constitutents present in coal as well as a detailed analysis of organic sulphur compounds present in flash evaporates and pyrolysates of a suite of coals ranging in sulphur content and degree of coalification reveals that the structure of organosulphur constituents in coal is very similar to that of organosulphur constituents present in bitumen and kerogen of sediments and in petroleums. Based on extensive knowledge with respect to the origin, nature and fate of organosulphur constituents in sediments and oils it is concluded that organosulphur constituents in coal are generated in the early stages of diagenesis (i.e. peat stage) by reaction of H2S or polysulphides (HSx−) with functionalized precursors yielding organ...
The identification of isoprenoid C₂₀ and C₁₅ sulphur compounds in Rozel Point Oil is described. A diagenetical scheme, indicating relationships between precursors and products is presented.
A number of selected molecular paraeters obtained from analysis
of immature crude oils and sediment extracts are evaluated as
indicators of palaeosalinity. The nature of these parameters is
discussed taking into account the role of intermolecular and
intramolecular incorporation of sulfur into specific functionalized
lipids. Specific distribution patterns of methylated chromans and
C₂₀ isoprenoid thiophenes and the relative abundance of
gammacerane are excellent indicators for palaeosalinity, whilst
other parameters such as 14α, (H), 17α(H)/14β (H), 17β (H) -sterane
ratios, the pristane/phytane ratio, the even-over-odd carbon number
predominance of n-alkanes and the relative abundance of C₃₅
hopanes and/or hopenes may indicate palaeohypersalinity but are
affected by environmental factors other than hypersalinity and by
diagenesis.
The molecular composition of five brown coals from three different basins (Maestrazgo, Mequinenza and Rubielos) in Spain was investigated by flash pyrolysis-gas chromatography and flash pyrolysis-gas chromatography-mass spectrometry. In these techniques, the macromolecular material is thermally degraded in an inert atmosphere and the compounds formed are on-line separated, identified and quantified. This information provided insight into the macromolecular structure of the coals which was inaccesible by other means. The composition of the pyrolysates is described in detail with emphasis on the distributions and relative abundance of n-alkanes, n-1-alkanes, (alkyl)phenols, sulphur compounds [(alkyl)thiophenes and (alkyl)benzenes and (alkyl)naphthalenes. These compound classes represent the major pyrolysis products of the samples analyse...
Porphyrins and related compounds are well known biological markers often applied in geochemistry.
