Evidence for enhanced mixing over rough topography in the abyssal ocean

The overturning circulation of the ocean plays an important role in modulating the Earth's climate. But whereas the mechanisms for the vertical transport of water into the deep ocean--deep water formation at high latitudes--and horizontal transport in ocean currents have been largely identified, it is not clear how the compensating vertical transport of water from the depths to the surface is accomplished. Turbulent mixing across surfaces of constant density is the only viable mechanism for reducing the density of the water and enabling it to rise. However, measurements of the internal wave field, the main source of energy for mixing, and of turbulent dissipation rates, have typically implied diffusivities across surfaces of equal density of only approximately 0.1 cm2 s(-1), too small to account for the return flow. Here we report measurements of tracer dispersion and turbulent energy dissipation in the Brazil basin that reveal diffusivities of 2-4 cm2 s(-1) at a depth of 500 m above abyssal hills on the flank of the Mid-Atlantic Ridge, and approximately 10 cm2 s(-1) nearer the bottom. This amount of mixing, probably driven by breaking internal waves that are generated by tidal currents flowing over the rough bathymetry, may be large enough to close the buoyancy budget for the Brazil basin and suggests a mechanism for closing the global overturning circulation.     

Effect of pretreatment with acetylsalicylate on surgical bleeding and peroperative mortality in rats undergoing kidney transplantation.

42 rats were pretreated with L-ASA before kidney transplantation, 43 rats acted as controls. 9 rats with L-ASA, but no control rats, died with i.p. haemorrhage. However, in animals surviving the operation, the intraoperative blood loss did not differ significantly between the 2 groups.     

Routing of anisotropic spatial solitons and modulational instability in liquid crystals

In certain materials, the spontaneous spreading of a laser beam (owing to diffraction) can be compensated for by the interplay of optical intensity and material nonlinearity. The resulting non-diffracting beams are called 'spatial solitons' (refs 1-3), and they have been observed in various bulk media. In nematic liquid crystals, solitons can be produced at milliwatt power levels and have been investigated for both practical applications and as a means of exploring fundamental aspects of light interactions with soft matter. Spatial solitons effectively operate as waveguides, and so can be considered as a means of channelling optical information along the self-sustaining filament. But actual steering of these solitons within the medium has proved more problematic, being limited to tilts of just a fraction of a degree. Here we report the results of an experimental and theoretical investigation of voltage-controlled 'walk-off' and steering of self-localized light in nematic liquid crystals. We find not only that the propagation direction of individual spatial solitons can be tuned by several degrees, but also that an array of direction-tunable solitons can be generated by modulation instability. Such control capabilities might find application in reconfigurable optical interconnects, optical tweezers and optical surgical techniques.     

Increased vascular prostacyclin activity in rats after endotoxin administration

Summary Endotoxin did not interact in vitro with prostacyclin activity but stimulated its release from vascular tissues when administered in single doses to rats 30 min before testing.Acknowledgments. This work was performed with the partial support of the Italian National Research Council (contract CNR 80-01086-83, Medicina Preventiva-Arteriosclerosi).     

Platelet aggregation by Thrombofax®. Studies on the mechanism of action

Résumé Le Thrombofax Ortho provoque l'agrégation des plaquettes humaines (ainsi que celles du chien, du cobaye et du rat) suite à la libération d'ADP endoplaquettaire. La¹⁴C-sérotonine et le facteur plaquettaire 4 sont aussi libérés au cours de la réaction. La fraction active du produit semble résider dans les acides gras libres.

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Supported in part by grant No. 1216 of the Fonds voor Geneeskundig Wetenschappelijk Onderzoek, Brussels.     

Effect of acetylsalicylate on surgical bleeding, postoperative mortality and allograft survival in rats undergoing heart transplantation.

18 rats were treated with L-ASA before heart transplantation and daily thereafter until death or rejection. 22 animals acted as controls. A significantly higher post-operative mortality rate, without any significant modification of the transplant survival time, was found in L-ASA-treated group.     

Etude de l'agrégation plaquettaire par le Thrombofax

Summary Thrombofax Ortho is a stable, reproducible, ready-to-use reagent for the evaluation of the platelet release reaction.

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Recherches effectuées avec l'appui financier du Fonds voor Wetensschappelijik Geneeskundig Onderzoek, Brussel (contrat No. 1216).     

Highly specialized mammalian skulls from the Late Cretaceous of South America

Dryolestoids are an extinct mammalian group belonging to the lineage leading to modern marsupials and placentals. Dryolestoids are known by teeth and jaws from the Jurassic period of North America and Europe, but they thrived in South America up to the end of the Mesozoic era and survived to the beginnings of the Cenozoic. Isolated teeth and jaws from the latest Cretaceous of South America provide mounting evidence that, at least in western Gondwana, dryolestoids developed into strongly endemic groups by the Late Cretaceous. However, the lack of pre-Late Cretaceous dryolestoid remains made study of their origin and early diversification intractable. Here we describe the first mammalian remains from the early Late Cretaceous of South America, including two partial skulls and jaws of a derived dryolestoid showing dental and cranial features unknown among any other group of Mesozoic mammals, such as single-rooted molars preceded by double-rooted premolars, combined with a very long muzzle, exceedingly long canines and evidence of highly specialized masticatory musculature. On one hand, the new mammal shares derived features of dryolestoids with forms from the Jurassic of Laurasia, whereas on the other hand, it is very specialized and highlights the endemic, diverse dryolestoid fauna from the Cretaceous of South America. Our specimens include only the second mammalian skull known for the Cretaceous of Gondwana, bridging a previous 60-million-year gap in the fossil record, and document the whole cranial morphology of a dryolestoid, revealing an unsuspected morphological and ecological diversity for non-tribosphenic mammals.