Tournaisian

The main elements that prompted the international community to use the Tournaisian as a name for the oldest stage of the Mississippian Subsystem are the same as those for the Viséan, i. e., the quality of exposures in southern Belgium, the diversity of facies, the pioneering palaeontological work that started in the mid 19th century and development of foraminiferal, conodont and rugose corals zonations in the last decades. The numerous Tournaisian sections in southern Belgium document a progressive change in environmental setting, from a ramp during the early Tournaisian to a shelf during the late Tournaisian. The spectacular late Tournaisian Waulsortian buildups that occurred within 2 third-order sequences had a strong impact on subsequent Viséan sedimentation. Recent advances in understanding the sequence stratigraphy has led to new insights on correlation between the central Dinant Sedimentation Area and more proximal areas

Moliniacian

The Moliniacian is the basal division of the Viséan in Belgium (regional Substage). Its base is identified by the entry of the foraminifer Eoparastaffella simplex in the Salet road section and correlates with the base of the Viséan Stage. Its top is defined by the base of the Livian Substage and coincides with a major bentonite, the ‘Banc d’or de Bachant’. It correlates with the late Chadian to Arundian of the British Isles and it provides a record of the final stage of the evolution of the Namur-Dinant Basin from a homoclinal ramp (in the Tournaisian) to a broad shelf of regional extend (end of the Moliniacian). It is characterized by varied facies reflecting different sedimentary environments across the basin and rich foraminifer and coral faunas that allow good biostratigraphic correlation. It is known from numerous sections in Belgium and Northern France

Ivorian

The Ivorian Substage is the upper division of the Tournaisian. Its base, emended in this paper, corresponds to the first appearance of the conodont Polygnathus communis carina in the Yvoir railway station section. Its top is defined by the base of the Moliniacian Substage which corresponds now to the base of the Viséan. The Ivorian is characterized by a rich and diversified conodont fauna throughout and by a diversification of the foraminifers in its upper part. It is therefore very well zoned and precisely correlated across the Franco-Belgian Basin and beyond. Its upper boundary is marked by a drastic reduction of the conodont fauna and the disappearance of selected Tournaisian foraminiferal taxa. Ivorian sedimentation reflects the evolution of the Namur-Dinant Basin from a homoclinal ramp in the early Tournaisian to a broad shelf of regional extent in the late Tournaisian. Waulsortian buildups started growing in the distal part of the ramp during early Ivorian and formed a discontinuous barrier over the southwestern part of the Dinant Sedimentation Area. Distal peri-Waulsortian facies are dominated by cherty crinoidal wacke- to packstones, thick-bedded crinoidal packtsones, grainstones and dolostones. An oolitic grainstone, the Avins Mbr of the Longpré Fm, caps the Ivorian succession in the inner shelf. Proximal peri-Waulsortian facies are cherty crinoidal wacke- to packstones and purplish blue, poorly fossiliferous wacke- to packstones

Viséan

The quality exposure of Viséan rocks in southern Belgium, the diversity of facies, the pioneer palaeontological works that started in the mid 19th century and the development of the foraminifer, conodont and rugose corals zonations in the last decades were the main elements for the promotion of the international use of the Viséan Stage. Southern Belgium is probably the best-documented area for the Viséan Stage in the world. In the Namur-Dinant Basin the submarine topographic irregularities inherited from the late Tournaisian and due to different sedimentation rates on the platform, in the basin and on the Waulsortian buildups were progressively smoothed out by the Viséan sedimentation. During the Tournaisian/Viséan transition, the central Dinant type area was in a peculiar, restricted environment and poorly fossiliferous, peri-Waulsortian facies developed. A new criterion for a better definition of the base of the stage was needed and has now been adopted. It is based on the evolutionary lineage of the foraminifer Eoparastaffella. A proposed new GSSP (Global Stratotype Section and Point) in Southern China (the Pengchong section) is still under discussion, but the term Viséan will remain as a stage corresponding to the Middle Series of the Mississippian Subsystem

Diffusive counter dispersion of mass in bubbly media

We consider a liquid bearing gas bubbles in a porous medium. When gas bubbles are immovably trapped in a porous matrix by surface-tension forces, the dominant mechanism of transfer of gas mass becomes the diffusion of gas molecules through the liquid. Essentially, the gas solution is in local thermodynamic equilibrium with vapor phase all over the system, i.e., the solute concentration equals the solubility. When temperature and/or pressure gradients are applied, diffusion fluxes appear and these fluxes are faithfully determined by the temperature and pressure fields, not by the local solute concentration, which is enslaved by the former. We derive the equations governing such systems, accounting for thermodiffusion and gravitational segregation effects which are shown not to be neglected for geological systems---marine sediments, terrestrial aquifers, etc. The results are applied for the treatment of non-high-pressure systems and real geological systems bearing methane or carbon dioxide, where we find a potential possibility of the formation of gaseous horizons deep below a porous medium surface. The reported effects are of particular importance for natural methane hydrate deposits and the problem of burial of industrial production of carbon dioxide in deep aquifers.Comment: 10 pages, 5 figures, 1 table, Physical Review

Natural Nuclear Reactor Oklo and Variation of Fundamental Constants Part 1: Computation of Neutronics of Fresh Core

Using modern methods of reactor physics we have performed full-scale calculations of the natural reactor Oklo. For reliability we have used recent version of two Monte Carlo codes: Russian code MCU REA and world wide known code MCNP (USA). Both codes produce similar results. We have constructed a computer model of the reactor Oklo zone RZ2 which takes into account all details of design and composition. The calculations were performed for three fresh cores with different uranium contents. Multiplication factors, reactivities and neutron fluxes were calculated. We have estimated also the temperature and void effects for the fresh core. As would be expected, we have found for the fresh core a significant difference between reactor and Maxwell spectra, which was used before for averaging cross sections in the Oklo reactor. The averaged cross section of Sm-149 and its dependence on the shift of resonance position (due to variation of fundamental constants) are significantly different from previous results. Contrary to results of some previous papers we find no evidence for the change of the fine structure constant in the past and obtain new, most accurate limits on its variation with time: -4 10^{-17}year^{-1} < d alpha/dt/alpha < 3 10^{-17} year^{-1} A further improvement in the accuracy of the limits can be achieved by taking account of the core burnup. These calculations are in progress.Comment: 25 pages, 14 figures, 12 tables, minor corrections, typos correcte

Acute success and short-term follow-up of catheter ablation of isthmus-dependent atrial flutter; a comparison of 8 mm tip radiofrequency and cryothermy catheters

Objectives: To compare the acute success and short-term follow-up of ablation of atrial flutter using 8 mm tip radiofrequency (RF) and cryocatheters. Methods: Sixty-two patients with atrial flutter were randomized to RF or cryocatheter (cryo) ablation. Right atrial angiography was performed to assess the isthmus. End point was bidirectional isthmus block on multiple criteria. A pain score was used and the analgesics were recorded. Patients were followed for at least 3 months. Results: The acute success rate for RF was 83% vs 69% for cryo (NS). Procedure times were similar (mean 144±48 min for RF, vs 158±49 min for cryo). More applications were given with RF than with cryo (26±17 vs. 18±10, p<0.05). Fluoroscopy time was longer with RF (29±15 vs. 19±12 min, p<0.02). Peak CK, CK-MB and CK-MB mass were higher, also after 24 h in the cryo group. Troponin T did not differ. Repeated transient block during application (usually with cryoablation) seemed to predict failure. Cryothermy required significantly less analgesia (p<0.01), and no use of long sheaths (p<0.005). The isthmus tended to be longer in the failed procedures (p=0.117). This was similar for both groups, as was the distribution of anatomic variations. Recurrences and complaints in the successful patients were similar for both groups, with a very low recurrence of atrial flutter after initial success. Concl

Developing an interatomic potential for martensitic phase transformations in zirconium by machine learning

Interatomic potentials: predicting phase transformations in zirconium Machine learning leads to a new interatomic potential for zirconium that can predict phase transformations. A team led by Hongxian Zong at Xi’an Jiaotong University, China, and Turab Lookman at Los Alamos National Laboratory, U.S.A, used a Gaussian-type machine learning approach to produce an interatomic potential that predicted phase transformations in zirconium. They expressed each atomic energy contribution via changes in the local atomic environment, such as bond length, shape, and volume. The resulting machine-learning potential successfully described pure zirconium’s physical properties. When used in molecular dynamics simulations, it predicted a zirconium phase diagram as a function of both temperature and pressure that agreed well with previous experiments and simulations. Developing learnt interatomic potentials in phase-transforming systems could help us better simulate complex systems

Mise en solution et précipitation de l'uranium et du thorium dans les conditions de moyenne et haute température (résumé)

Les études tant analytiques qu'expérimentales réalisées au cours des vingt dernières années ont bien montré le rôle joué par les complexes d'uranylcarbonates dans le transport de l'uranium en milieu hydrothermal oxydant ou faiblement réducteur. Les travaux expérimentaux actuels sur la mobilité de U et Th, à haute température et haute pression, montrent la très grande différence de solubilité entre UO2 et ThO2, comme l'influence des ions complexants et celles de fO2 et aH+. Ces résultats expérimentaux sont comparés aux données recueillies sur les leucogranites et les granites calcoalcalins (France) et divers gisements ou anomalies en uranium (Québec, Rössing, Madagascar, etc.). Dans la catazone U et Th précipitent sous forme de solutions solides d'uranothorianite dans les milieux déficitaires en silice, et sous forme d'uranothorite dans les granites et les syénites La précipitation d'uraninite non thorifère dans les leucogranites français s'explique d'abord par la faible concentration en thorium des solutions aqueuses durant la phase deutérique. Au cours du métamorphisme progressif on peut observer un retard dans la mobilisation de l'uranium en conditions relativement oxydantes, quand U est associé à Ti et OH. Dans le domaine mésozonal la brannérite stabilise l'uranium en présence de titane jusqu'à l'anatexie. Au-delà elle se dissocie en donnant de l'uraninite non thorifère et du rutile