Showing papers by "École Normale Supérieure published in 1969"

The Structure of High-Angle Grain Boundaries in Aluminium

Abstract: A transmission electron-microscopy study of high-angle grain boundaries has been made. When thin foils are cut in precisely oriented bicrystals of aluminium, some details of the grain-boundary structure appear. Micrographs of symmetrical tilt boundaries around [001] show linear defects parallel to the tilt axis. Their properties are tightly bound to the geometry of the bicrystal: this provides a good support to the idea of a transitional lattice as a structure of a high-angle boundary. A theoretical interpretation of these observations is developed essentially on geometrical considerations.

Evidence for Rb-Rare-Gas Molecules from the Relaxation of Polarized Rb Atoms in a Rare Gas. Theory

Abstract: Relaxation experiments performed on optically polarized Rb atoms in a rare gas have been previously reported; their detailed interpretation is given below. It is shown that the relaxation governed by the spin-orbit interaction is strongly affected by the formation of chemically unstable Rb-Kr molecules bound by van der Waals forces. Two processes of molecule formation are analyzed: binary resonant collisions leading to metastable states and three-body collisions producing actual bound states. A relaxation model valid for any disorientation probability per single Rb-Kr interaction is developed. Aside from clear evidence for the existence of alkali-rare-gas molecules, the success of the theoretical interpretation of the relaxation experiments yields the equilibrium constant $\mathcal{K}=1.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}22}$ ${\mathrm{cm}}^{3}$/molecule for the reaction Rb+Kr \ensuremath{\rightleftharpoons} Rb-Kr at 300\ifmmode^\circ\else\textdegree\fi{}K, the average lifetime of a Rb-Kr molecule in the gas phase, $\ensuremath{\tau}=0.65\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ sec, at a krypton pressure of one Torr, and the average spin-orbit coupling constant in a Rb-Kr molecule, $\overline{\ensuremath{\gamma}}{h}^{\ensuremath{-}1}=0.63$ MHz. It is also shown that the spin-orbit potential is predominantly short-range.

Simulation du mouvement brownien d'une chaine macromoléculaire par la méthode de Monte-Carlo.

Abstract: Une simulation du mouvement brownien d’une chaine macromoleculaire est realisee en construisant la chaine dans un reseau tetraedrique et en lui faisant subir, a l’interieur, des mouvements de 3 et 4 liaisons, et aux extremites, des mouvements de 1 et 2 liaisons. Le programme de simulation fournit l’analyse de nombreux parametres qui permettent de suivre l’evolution de la conformation de la chaine, de ses dimensions caracteristiques, des deplacements des atomes et des mouvements des liaisons.

A1-Nucleon Cross Section from Coherent Production in Nuclei

Abstract: Comparison of ${A}_{1}$ coherent production in Freon with production in ${\mathrm{H}}_{2}$ implies a total ${A}_{1}$-nucleon cross section $\ensuremath{\sigma}({A}_{1}N)l~({0.5}_{\ensuremath{-}0.2}^{+0.3})\ensuremath{\sigma}(\ensuremath{\pi}N)$ with a further theoretical uncertainty of about 10%. The result appears to preclude the possibility, suggested by the Deck model, that the $\ensuremath{\rho}$ and $\ensuremath{\pi}$ in the ${A}_{1}$ are produced close together without appreciable interaction between them.

Le développement du télencéphale d'un poisson osseux primitif, Polypterus senegalus Cuvier

Abstract: Resume Les resultats de l'analyse du developpement embryonnaire du telencephale de Polypterus senegalus, ainsi que d'une courte description du telencephale de l'adulte ont ete compares aux donnees presentes dans la litterature scientifique, concernant le developpement et la structure du telencephale des Chondrosteens (Ch), des Holosteens (H) et des Teleosteens (T). Par l'organogenese et la morphologie de son telencephale, Polypterus presente de nombreux points de ressemblance avec les trois groupes ci-dessus cites. Dans la liste des resultats qui vont etre donnes, nous avons adopte le principe suivant: si le processus de developpement ou la structure dont il est fait mention concerne non seulement Polypterus, mais aussi les autres groupes de Poissons osseux, les initiales de ces groupes (Ch, H, T) seront ajoutees entre parentheses. 1 Comme chez tous les Gnathostomes, la morphogenese du telencephale du Polyptere commence par une inversion legere de ses parois laterales. 2 Par la suite, cette inversion, disparait. Les parois de l'ebauche telencephalique commencent a faire saillie dans la cavite ventriculaire et, correlativement, les taeniae (c'est-a-dire les deux lignes le long desquelles se rattache le toit telencephalique originellement etroit) se deplacent lateralement (H, T). 3 Ulterieurement, les taeniae se deplacent en direction ventrale, et l'apparition de sillons externes bilateraux (sulcus externus) indique les debuts du processus d'eversion (Ch, H, T). 4 Chez les Chondrosteens, les Holosteens et les Teleosteens, c'est l'epaississement des parois telencephalique qui domine pendant reversion; chez Polypterus au contraire, ces parois croissent bien plus suivant leur dimension dorsoventrale qu'en epaisseur. 5 Les bulbes olfactifs apparaissent au debut sous forme d'epaississements des parois telencephaliques. Plus tard, ils prennent la forme d'evaginations separees, possedant en propre leur cavites ventriculaires (Ch, H). 6 Outre reversion et l'evagination reelle bulbaire, une pseudoevagination (Kallen) se produit dans le telencephale de Polypterus. Ce processus conduit a la formation d'un septum ependymaire etendu (Ch, H). 7 Tot au cours du developpement, deux regions, qui sont respectivement l'area dorsalis telencephali ou pallium et l'area ventralis telencephali ou subpallium, peuvent etre distinguees d'apres des differences cytologiques (Ch, H, T). 8 La zone periventriculaire de l'area ventralis telencephali se differencie en un nucleus subpallialis dorsalis et un nucleus subpallialis ventralis (Ch, H, T). D'autres cellules de l'area ventralis migrent vers une position submeningee et forment un noyau subpallialis lateralis (H, T). 9 Une colonne de cellules migrantes dirigee rostroventralement, et provenant de la portion la plus dorsocaudale du manteau subpallie, aboutit a la formation du complexe des noyau entopedonculaires (Ch, H, T). 10 Dans l'area dorsalis telencephali du Polyptere, la couche du manteau embryonnaire persiste chez l'adulte sous forme d'une zone etroite de substance grise periventriculaire. Cette zone ne montre ni aux stades larvaires, ni chez l'adulte, de signe de differenciation en territoires distincts. 11 L'area dorsalis telencephali ou pallium du Polyptere montre un stade d'organisation bien plus simple que celui des Chondrosteens, des Holosteens et des Teleosteens. 12 Une couche cellulaire externe etendue se forme dans la partie rostrale evaginee du telencephale du Polyptere. Comme chez Acipenser, cette couche est en continuite avec la zone glomerulaire et appartient integralement a la formation bulbaire. Abstract In this paper an analysis of the development of the forebrain of Polypterus senegalus, and a short description of the adult telencephalon of that species has been presented. The results of this study have been compared with data obtained from the literature on the development and structure of the forebrain of the Chondrostei (Ch), Holostei (H), and Teleostei (T). It appeared that, with regard to the embryology and morphology of its forebrain, Polypterus shows many points of resemblance to the three groups mentioned. In the subsequent survey of results these similarities have been indicated as follows: if the process or feature mentioned occurs not only in Polypterus, but also in the other bony fish groups, the initials of these groups (Ch, H, T) are added in brackets. 1 As in all Gnathostomes the morphogenesis of the forebrain of Polypterus commences with a slight inversion of its lateral walls. 2 During further development this inversion disappears. The walls of the telencephalic anlage begin to protrude into the ventricular cavity, and concomitantly the taeniae (i.e. the lines of attachment of the initially narrow telencephalic roof plate) move laterally (H, T). 3 Later the taeniae are displaced ventrally, and the appearance of bilateral external grooves (sulci externi) marks the beginning of an eversion (Ch, H, T). 4 In the Chondrostei, Holostei and Teleostei the thickening of the telencephalic walls continues during the eversion, but in Polypterus these walls increase much more in dorsoventral length than in thickness. 5 The bulbi olfactorii develop initially as thickenings of the telencephalic walls. In later stages they assume the configuration of separate evaginations, with ventricular cavities of their own (Ch, H). 6 Apart from eversion and true evagination, an extensive pseudoevagination (Kallen) occurs in the forebrain of Polypterus. This process leads to the formation of an extensive ependymal septum (Ch, H). 7 Early in development two regions, i.e., the area dorsalis telencephali or pallium and the area ventralis telencephali or subpallium can be delimited on account of cytological differences (Ch, H, T). 8 The periventricular zone of the area ventralis telencephali differentiates into a nucleus subpallialis dorsalis and a nucleus subpallialis ventralis (Ch, H, T). Other cells within the area ventralis migrate to a submeningeal position and form a nucleus subpallialis lateralis (H, T). 9 A rostroventrally directed migration of cells, originating from the most dorsocaudal part of the subpallial mantle layer, leads to the formation of a complex of entopeduncular nuclei (Ch, H, T). 10 In the area dorsalis telencephali of Polypterus the embryonic mantle layer persists as a narrow zone of periventricular gray. Neither in the larvae nor in the adult does this zone show signs of a differentiation into separate fields. 11 The area dorsalis telencephali or pallium of Polypterus is much more simply organized than that of the Chondrostei, Holostei and Teleostei. 12 In the rostral, evaginated part of the forebrain of Polypterus an extensive external cell layer is formed. As in Acipenser this layer is coextensive with the glomerular zone and belongs entirely to the bulbar formation.

Detection of Al 2 O 3 : Fe 2+ by Acoustic Paramagnetic Resonance

Abstract: We have observed acoustically a spin-resonance line that we believe is due to the ground state of ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$: ${\mathrm{Fe}}^{2+}$. This spin system has not previously been detected by resonance techniques. The transition has a ${g}_{\mathrm{II}}$ of 3.40\ifmmode\pm\else\textpm\fi{}0.04, and its variation with magnetic field direction suggests that a singlet level is also present, at an energy, when the field is parallel to the $c$ axis, of not less than 6 ${\mathrm{cm}}^{\ensuremath{-}1}$ above the ground doublet. From the intensity of the line, it was estimated that the magneto-elastic coefficient ${[\frac{1}{4}{({G}_{11}\ensuremath{-}{G}_{12})}^{2}+{{G}_{16}}^{2}]}^{\frac{1}{2}}$ has a value of not less than 15 ${\mathrm{cm}}^{\ensuremath{-}1}$ ${(\mathrm{unit}\mathrm{strain})}^{\ensuremath{-}1}$. These results are consistent with recent calculations by Stevens and Walsh.

Point de charge nulle et structure des silicates

Abstract: La determination du point de charge nulle des silicates a l’aide de la mesure du potentiel electrocinetique par la methode du potentiel d’ecoulement effectuee avant et apres le traitement acide des surfaces permet de mettre en evidence une relation tres etroite entre la structure des silicates etudies et la valeur correspondante de leur point de charge nulle (P.C.N). La classification structurale des silicates est fondee sur le mode d’arrangement des tetraedres (SiO4 )4- . Cette trame confere aux silicates certaines proprietes essentielles dont notamment les clivages qui apparaissent apres broyage. Sur ces clivages, le rapport cations/Si determine la valeur du point de charge nulle du mineral considere.

Aménagement Caprivari-Cahoeira étude en charge

Abstract: This article refers to the design studies and work done in constructing the pressure shaft in the Capivari-Cachoeira hydro-power scheme, which has an installed output of 250,000 kW. The shaft operates under pressures of up to 85 kg/cm2. Its diameter is 3.0 m in the upper unlined portion and 2.90 m in the lined portion below it. The article begins with a theoretical study of stresses in indefinite porous ground out of which a cylindrical cavity has been hollowed out and filled with water under a constant pressure. The ground thus contains a flow, the resulting loss of head being simply considered as an additional volume force acting at all points in the ground. The calculation result confirms the Bratz theorem which states that the forces acting at any point are defined simply by adding the percolating flow pressure and the stresses in the ground, assuming pressure to be only applied on the surface. The discrepancies between the resulting conclusion and the results of two other investigations are explained by calculation : the strain assumptions differ in each case, but each has its own particuar field of application. A theoretical study of the effect of grouting on the percolating flow characteristics is then described. Next, the results of pressure tests on a cavity under conditions which are seldom if ever attained in practice are discussed. The cavity was 15 m long, with a diameter of 2.20 m and was subjected to a pressure of 65 kg/cm2. The test was also appllied to the cavity with unlined sides, then with a concrete lining grouted under high pressure. The load with stood by the rock was found to he practically the same in both cases, with little difference between the respective leakage rates. The analysis of losses over a period of time confirmed the results of a theoretical interpretation of these effects, it having been found that the filling of the ground with water appeared to reduce the losses, i.e. an effect which is generally ignored in standard tests on small-diameter wells. These tests were completed by tests in which small-diameter boreholes were put under pressures of up to as much as 100 kg/cm2 by the classical Lugeon test method. The results obtained are compared with the experimental cavity data. This enabled the upper limit of the lined shaft portion to be determined, which was found to be at a point at which the maximum static head was 400 m of water. Finally, the calculations whereby the lining thickness in the lower shaft portions were determined are discussed. These calculations as conventiona1 as regards internal pressures, but an original solution was found to the outside pressure problem which consisted in sinking a shaft running parallel to the lined shaft and providing drainage borings to eliminate dangerous water pressure in the ground when emptying the system.