Search results

3,414 records were found.

The basic structure and stereochemistry of the characteristic glycerol dibiphytanyl glycerol tetraether (GDGT) membrane lipid of cosmopolitan pelagic crenarchaeota has been identified by high field two-dimensional (2D)-NMR techniques. It contains one cyclohexane and four cyclopentane rings formed by internal cyclisation of the biphytanyl chains. Its structure is similar to that of GDGTs biosynthesized by (hyper)thermophilic crenarchaeota apart from the cyclohexane ring. These findings are consistent with the close phylogenetic relationship of (hyper)thermophilic and pelagic crenarchaeota based 16S rRNA. The latter group inherited the biosynthetic capabilities for a membrane composed of cyclopentane ring-containing GDGTs from the (hyper)thermophilic crenarchaeota. However, to cope with the much lower temperature of the ocean, a small bu...
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...
Continuous seismic reflection data show that there are no unconsolidated sediments on the outer part of the Irish continental shelf west of Donegal Bay and on the upper part of the slope. Both the “basement” and the sediment cover on the lower part of the slope are heavily intersected, presumably by faults.
The lowermost Devonian beds in Gotland (Sweden) were deposited in a very shallow marine environment, close to the coast. In these beds three structures were observed, whose mode of formation cannot be explained by the author.
In the past decade, tomographic imaging has revealed that trajectories of mantle convection are more complex than expected from end-member models of unhindered whole mantle circulation or layered convection with an interface at 660 km depth. In the context of recently proposed mantle flow models, we discuss evidence for compositional heterogeneity in the deepest 1000 km of the mantle, and describe how this could survive in a system of thermochemical convection.
High discharges in the Dutch Rhine branches have initiated large explorative studies to suggest alternative ways of river management. These studies need detailed information on the morphological behaviour of rivers: especially information on the sediment transport dynamics at river bifurcations is wanted, for possible changes in the sediment distribution at river bifurcations have implications for all parts of the downstream area. The present study focuses on the heavily engineered IJsselkop bifurcation, the location where the Pannerdensch Kanaal distributes into the rivers IJssel and Nederrijn. The IJsselkop is situated in the eastern part of the Netherlands, and is characterised by bimodal bed sediments (modes at 0.7 mm and 7 mm). The aims of this study were to determine the influence of discharge variations, weir management and rive...
A comparison is made between the approach of the data on gravity and heat flow by the concepts of Wunderlich (1966) and the present author (Van Bemmelen, 1966). Wunderlich's model of physical interpretation is based on an erroneous idea of the meaning of the form of the geoid, as determined by artificial satellites. The new model of the earth's evolution, presented by the author, offers a promising way of interpretation, which is based on physico-chemical principles.
A description of Adoxa moschatellina pollen.
"Unfortunately a dichotomy has developed in paleontology, with the morphological systematists on one branch and the ecologists on the other. The former commonly regard the latter as impractical theorizers who are unable or unwilling to read the vast mountain of relevant literature, while the latter commonly regard the systematists as hopelessly old-fashioned museum paleontologists, who only think of fossils as specimens in drawers. In my opinion a training period of purely morphological work is essential to every paleontologist, but there is no need for this to have a fossilizing effect on the student of fossils. If paleontology is to progress beyond the level of stamp collecting, we must consider fossils as living organisms. The museum and the library are excellent places to study paleontology, but so are the laboratory, the cliff, an...
Want to know more?If you want to know more about this cutting edge product, or schedule a demonstration on your own organisation, please feel free to contact us or read the available documentation at http://www.keep.pt/produtos/retrievo/?lang=en