Prospectives

Tiré de: Prospectives, vol. 15, no 3, oct. 1979.Titre de l'écran-titre (visionné le 24 janv. 2013

Prospectives

Tiré de: Prospectives, vol. 22, no 3, oct. 1986Titre de l'écran-titre (visionné le 24 janv. 2013

Prospectives

Tiré de: Prospectives, vol. 20, no 4, déc. 1984Titre de l'écran-titre (visionné le 24 janv. 2013

Rotation and lithium abundance of solar-analog stars. Theoretical analysis of observations

Rotational velocity, lithium abundance, and the mass depth of the outer convective zone are key parameters in the study of the processes at work in the stellar interior, in particular when examining the poorly understood processes operating in the interior of solar-analog stars. We investigate whether the large dispersion in the observed lithium abundances of solar-analog stars can be explained by the depth behavior of the outer convective zone masses, within the framework of the standard convection model based on the local mixing-length theory. We also aims to analyze the link between rotation and lithium abundance in solar-analog stars. We computed a new extensive grid of stellar evolutionary models, applicable to solar-analog stars, for a finely discretized set of mass and metallicity. From these models, the stellar mass, age, and mass depth of the outer convective zone were estimated for 117 solar-analog stars, using Teff and [Fe/H] available in the literature, and the new HIPPARCOS trigonometric parallax measurements. We determine the age and mass of the outer convective zone for a bona fide sample of 117 solar-analog stars. No significant on-to-one correlation is found between the computed convection zone mass and published lithium abundance, indicating that the large A(Li) dispersion in solar analogs cannot be explained by the classical framework of envelope convective mixing coupled with lithium depletion at the bottom of the convection zone. These results illustrate the need for an extra-mixing process to explain lithium behavior in solar-analog stars, such as, shear mixing caused by differential rotation. To derive a more realistic definition of solar-analog stars, as well as solar-twin, it seems important to consider the inner physical properties of stars, such as convection, hence rotation and magnetic properties.Comment: 9 pages, 7 figure

Front propagation into unstable and metastable states in Smectic C* liquid crystals: linear and nonlinear marginal stability analysis

We discuss the front propagation in ferroelectric chiral smectics (SmC*) subjected to electric and magnetic fields applied parallel to smectic layers. The reversal of the electric field induces the motion of domain walls or fronts that propagate into either an unstable or a metastable state. In both regimes, the front velocity is calculated exactly. Depending on the field, the speed of a front propagating into the unstable state is given either by the so-called linear marginal stability velocity or by the nonlinear marginal stability expression. The cross-over between these two regimes can be tuned by a magnetic field. The influence of initial conditions on the velocity selection problem can also be studied in such experiments. SmC$^*$ therefore offers a unique opportunity to study different aspects of front propagation in an experimental system

Les fonctions du groupe dans les cours postsecondaires à distance selon des adultes franco-ontariens /

Thèse présentée à la Faculté des études supérieures en vue de l'obtention du grade de Ph. D. en andragogie.Ph. D. Université de Montréal 2005Bibliographie : pages 266-294

Cronoestratigrafía del volcanismo con énfasis en ignimbritas desde hace 25 Ma en el SO del Perú – Implicaciones para la evolución de los Andes centrales

El sur del Perú representa el segundo campo ignimbrítico de los Andes con un área que sobrepasa los 25 000 km2 y volúmenes de casi 5000 km3. Se prresenta la extensión, la estratigrafía y la cronología de 12 ignimbritas que afloran en el área de los cañones profundos de los Ríos Ocoña–Cotahuasi–Marán y Colca (OCMC). La cronología de las ignimbritas a lo largo de los últimos 25 Myr está basada en 74 dataciones 40Ar/39Ar and U/Pb. Antes de 9 Ma, ocho ignimbritas con gran volumen fueron producidas cada 2.4 Myr. Después de 9 Ma, el periodo de reposo entre cada ignimbrita de volumen pequeño a moderado ha disminuido hasta 0.85 Myr. Esta cronología de las ignimbritas y de las lavas del Neógeno y Cuaternario ayuda a revisar la nomenclatura de las formaciones volcánicas utilizadas para la Carta Geológica Nacional. Además las unidades volcánicas identificadas son herramientas para reconstruir la evolución geológica del flanco occidental de los Andes Centrales durante su levantamiento desde hace 25 Ma. Junto con la cronoestratigrafía de estas unidades, datos geomorfológicos obtenidos en las cuencas y sobre otros depósitos de los cañones OCMC ayudan a precisar la historia de la incisión del flanco occidental de los Andes Centrales desde hace 25 Ma. Finalmente la cronología de depósitos de avalancha de escombros y de terrazas rocosas basada en cosmogénicos (Be10) permite precisar la evolución de los cañones durante el Pleistoceno y el Holoceno

Transposing MISA Learning Scenarios into IMS Units of Learning

Commentary on: Chapter 17: Applying Learning Design to Supported Open Learning. (McAndrew & Weller, 2005) Abstract: This paper reports an exploratory study investigating the transposition process of a course called the Black Box into a Unit of Learning (UoL), characterized by its collaborative and multi-actor distance learning scenario. It was graphically represented by using the MOT software used in the MISA Instructional Engineering Method. To transpose this scenario into an IMSLD UoL, the iterative nature of this study helped develop the MOT+LD editor and an IMSLD Graphical Representation Code (GRC) now embedded in the editor. The study showed that the MISA method and Level A of the IMSLD Specification share several conceptual elements and representations that accentuate their complementarity in a coherent and clear manner. This finding is very encouraging to extend the analysis of levels B and C of the specification and adapt the MISA method to ease the construction of fully interoperable IMSLD UoL. Editors: Colin Tattersall and Rob Koper

Flexible Pad Bearing System For A High Speed Centrifugal Compressor

LecturePg. 57-64The application of a new radial and thrust bearing for use in high speed integrally geared centrifugal compressors is presented. The bearing design is of the flexible pad type. Bearing design analyses were conducted to assure a stable rotor bearing system, along with possible improvement in bearing performance relative to the five shoe tilting pad journal bearing and taperland thrust bearing system. Performance characteristics of both the radial and thrust bearings were measured at different bearing loads, and compared with the predicted results. Comparison of the bearing performance parameters were also made with the five shoe tilting pad journal and taperland thrust bearing system. Performance parameters included lubricant temperature rise between the oil inlet and discharge, oil flow, frictional power loss, and bearing pad metal temperature. Rotor bearing stability characteristics were evaluated at different loads to assure and verify a stable rotor bearing configuration. Predicted rotor response was also compared with those obtained during the test. The test results showed that the flexible pad bearing system resulted in a lower oil temperature rise, and frictional power loss over the five shoe tilting pad journal and taperland thrust bearing system. The flexible pad rotor bearing system was also found to be stable, and that the observed peak response correlated well with prediction