15 research outputs found
Behavior of central plasma relaxation oscillations during localized electron cyclotron heating on the TCV tokamak
L'insuffisance mitrale chronique et ses r\ue9percussions sur le ventricule et l'oreillette gauches
1,1-Bi(trishomobarrelenyl) - Synthesis and Chiroptic Properties
1,1-Bi(endo,exo,syn-pentacyclo[3.3.3.02,4.06,8.09,11]undecyl)[1,1-bi(trishomobarrelenyl)] (4) has been prepared as a 1:1 mixture of its meso- and d,l-diastereomers in six steps from trishomobarrelene 1 via the amine 5, the N,N-bis(trishomobarrelenyl)sulfamide 6 and the 1,2-(trishomobarrelenyl)diazene 7 in 16 % overall yield. Crystals of meso-4 were grown from a pentane solution of the mixture and subjected to an X-ray structure analysis. The (+)- and the (-)-enantiomer were isolated by HPLC on a chiral-phase column. They exhibited significantly enhanced molar optical rotations which are consistent with the presence of three helically arranged 1,2-dicyclopropylethane units in their skeletons. The absolute configuration of the (+)-enantiomer was assigned on the basis of DFT computed optical rotations of both enantiomers to be all-(S)
A shift from lithostratigraphic to allostratigraphic classification of Quaternary glacial deposits
Palynology and Microfacies of Lower Devonian Mixed Carbonate-Siliciclastic Deposits in Podolia, Ukraine
On the tracks of the earliest dinosaurs: implications for the hypothesis of dinosaurian monophyly
From the record of dinosaurian skeletal remains it has been inferred that the origin and initial diversification of dinosaurs were rapid events, occupying an interval of about 5 million years in the Late Triassic. By contrast numerous reports of dinosauroid tracks imply that the emergence of dinosaurs was a more protracted affair extending through much of the Early and Middle Triassic. This study finds no convincing evidence of dinosaur tracks before the late Ladinian. Each of the three dinosaurian clades - Theropoda, Sauropodomorpha, Ornithischia - produced a unique track morphotype that appears to be an independent modification of the chirotherioid pattern attributed to stem-group archosaurs (thecodontian reptiles). The existence of three divergent track morphotypes is consistent with the concept of dinosaurian polyphyly but can be reconciled with the hypothesis of dinosaurian monophyly only by invoking many and rapid reversals in the locomotor anatomy of early dinosaurs. The origin of dinosaurs was not the correlate or consequence of any single event or process, be it global change, competitive replacement, or opportunism in the wake of mass extinction. Instead the origin of dinosaurs is envisaged as a series of three cladogenetic events over an interval of at least 10 million years and possibly as much as 25 million years. This scenario of dinosaurian polyphyly is as well-supported by fossil evidence as is the currently favoured view of dinosaurian monophyly