Showing papers by "University of Rennes published in 1973"

Petrography of the Sokoman Iron Formation in Part of the Central Labrador Trough, Quebec, Canada

Abstract: The sedimentary textures of the Sokoman Iron Formation are similar to those of limestones; therefore the classification of textural elements in limestone (Folk) can be applied to the iron formation. The authors recognized the following textural elements: (a) femicrite (a matrix of iron silicate and carbonate) and matrix chert, both analogous to micrite; (b) cement chert and carbonatic cements; (c) aggregated particles, comparable to Folk9s allochems: pellets, intraclasts, ooliths, and pisolites. Shard textures are derived from ooliths and intraclasts by compaction. Rock types are defined by the combination of textural elements they contain. The iron formation suffered extensive epigenetic alteration. Dessiccation, shrinkage of silica-gel, compaction, and cementation are early diagenetic. Primocrystallization of quartz concludes the early diagenetic stage. It leads through a cryptocrystalline stage to the end phase of micropolygonal quartz. Quartz re-crystallized further during late diagenesis (burial metamorphism?) and again during a synkinematic to postkinematic regional metamorphism. Hematite dust is the oldest iron oxide. Much of the microscopic magnetite and specularite formed during early diagenesis. Migration of iron occurred; iron has been enriched in magnetite- or hematite-rich layers (“metallic” layers) during early diagenesis. Renewed crystallization of iron oxides occurred during the regional metamorphism. Microgranular siderite is perhaps primary. Porphyroblasts and glomero-porphyroblastic concretions of siderite, ankerite, and ferriferous calcite are early diagenetic. Minnesotaite and stilpnomelane are late diagenetic minerals. Riebeckite (and perhaps talc) formed during the regional metamorphism.

Geotectonic Model for the Iberian Variscan Orogen

Abstract: A diagrammatic cross section shows the gross structure of the Iberian variscan orogen has a fan-like pattern with outwards vergences and thrusting in the external zones. A brief analysis of the geotectonics of this chain shows differences that reflect an unusual crustal evolution.

Nishimoto's disease: significance of its angiographic appearances.

Abstract: The authors conclude, on the basis of personal cases and despite several unanswered questions, that the angiographic picture known as Nishimoto's disease, covers two distinct entities, viz. a true congenital disease characterized by arterial stenosis occurring early in embryonal development, with persistence of a patent arterial capillary network at the base of the skull which plays a part as a collateral pathway for the cerebral blood flow, and secondly, angiographic appearances which are similar but unilateral in distribution, related to acquired stenosis of the main arterial trunks. Only the first group should be called Nishimoto's disease.

Observations sur le développement larvaire de Nyctiphanes couchii (Crustacea: Euphausiacea) au laboratoire

Abstract: 1. Les larves de Nyctiphanes couchii (Bell) ont ete elevees au laboratoire, a partir des stades calyptopis II et III, en utilisant des regimes alimentaires animaux vegetaux et mixtes. 2. N. couchii se nourrit par predation et par filtration des la phase calyptopis. 3. L'etude a permis de recueillir des informations sur l'ontogenese des larves (developpement des appendices, formation des photophores, reduction du nombre d'epines du telson). 4. La vitesse de croissance peut atteindre 0,13 mm par jour, en moyenne, dans les lots nourris de nauplii d'Artemia salina. 5. La duree du stade calyptopis III est de 3,7 jours, en moyenne, et celle des stades furcilia est generalement comprise entre 3 et 4 jours, sous nos conditions d'elevage. La duree des stades tend a s'allonger lorsque les larves vieillissent. 6. Les regimes alimentaires a base d'algues permettent une croissance plus faibe que les nauplii d'A. salina et provoquent und allongement des intermues et de l'ontogenese. Un apport limite de nauplii d'A. salina produit des effects comparables.

Ultrasonic patterns of tumors of the liver.

Abstract: This study deals with the ultrasonic analysis of tumors of the liver and involves 85 cases of anatomically confirmed neoplasms. We shall describe four specific patterns of cancer: the large, highly echogenic nodule, anechoic nodules surrounded by a band of echoes, which correspond to necrotic, metastatic nuclei; the indistinct, transonic region within in echogenic parenchyma, often found in cancers observed in the course of cirrhosis; the large, entirely homogeneous hepatomegaly, which is the normal pattern of primary cancers, but which can be mistaken for a fluid collection. We consider that accurate information about these patterns may lead to a more reliable and precise diagnosis.

Raman Scattering by α‐HgS (Cinnabar)

Abstract: Raman scattering is observed in first and second order by optically active phonons in mercury sulphide HgS having the cinnabar structure (α-HgS). For the first time these spectra could be obtained in polarised light and interpreted using selection rules derived by group theoretical considerations. The experiments have been performed both at room temperature and at low temperatures (90 °K). Nous avons etudie la diffusion Raman au premier et second ordre par les phonons optiquement actifs du sulfure de mercure HgS ayant la structure cinabre (α-HgS). Pour la premiere fois, ces spectres ont ete obtenus en lumiere polariaee et interpretes a l'aide des regles de selection derivees de la theorie des groupes. Les experiences ont ete faites a la tempearature ambiante et e 90 °K.

Optical properties of thin lead films in the energy range 3-15.5 eV evaporated and studied in ultrahigh vacuum

Abstract: Reflectance measurements, in situ, on freshly deposited thin lead films are carried out in the far uv. Optical constants and other useful functions such as ${\ensuremath{\epsilon}}_{1}$, ${\ensuremath{\epsilon}}_{2}$, $\ensuremath{-}\mathrm{Im}({\ensuremath{\epsilon}}^{\ensuremath{-}1})$, $\ensuremath{-}\mathrm{Im}{(\ensuremath{\epsilon}+1)}^{\ensuremath{-}1}$ are deduced. The existence of volume and surface plasmons is demonstrated. The structure of ${\ensuremath{\epsilon}}_{2}$ is attributed to interband transitions both at critical points and between parallel bands; for the latter there is reasonable agreement between the experimental data and Ashcroft's calculation.

Réflectivité infrarouge du cinabre synthétique (α‐HgS)

Abstract: Nous avons mesure a T = 300 et 80 K les spectres de reflectivite infrarouge du cinabre (α-HgS) en lumiere polarisee. Pour la premiere fois, tous les modes de vibrations prevus par la theorie des groupes ont ete observes et analyses en termes d'oscillateurs. Ces experiences ont ete effectuees sur un cristal synthetique de bonne qualite. Elles completent les resultats anterieurs et conduisent a un modele satisfaisant pour la dispersion de la constante dielectrique. Infrared reflectivity spectra of cinnabar (α-HgS) have been recorded in polarized light at 300 and 80 K. For the first time all the vibration modes predicted by group theory have been observed and analysed in terms of oscillators. The experiment has been performed on a synthetic crystal of good quality. It leads to a better knowledge of the lattice dynamics and of the dispersion of the dielectric constant.

Gestion Optimale d'un Ordinateur Multiprogramme à Mémoire Virtuelle

Abstract: Les resultats cites plus haut montrent l'interet de mettre en oeuvre un mecanisme de controle dynamique qui regle le degre de multiprogrammation en fonction de la charge du systeme et du comportement de la B.M. L'etape suivante du developpement de cet outil doit permettre de preciser les conditions de son implantation a l'aide des simulations detaillees du systeme complet qui decrivent precisement les mecanismes de pagination et d'E/S afin d'evaluer les valeurs de Δ, periode de commande de l'interrupteur, et de la periode d'estimation qui realisent le compromis optimal entre le cout des operations de commande et d'estimation, et l'amelioration des performances qui en decoulent.