Showing papers by "École Polytechnique de Montréal published in 1976"

Maximal Closure of a Graph and Applications to Combinatorial Problems

Abstract: This paper generalizes the selection problem discussed by J. M. Rhys [Rhys, J. M. W. 1970. Shared fixed cost and network flows. Management Sci.17 3, November.], J. D. Murchland [Murchland, J. D. 1968. Rhys's combinatorial station selection problem. London Graduate School of Business Studies, Transport Network Theory Unit, Report LBS-TNT-68, June 10.], M. L. Balinski [Balinski, M. L. 1970. On a selection problem. Management Sci.17 3, November.] and P. Hansen [Hansen, P. 1974. Quelques approches de la programmation non lineaire en variables 0-1. Conference on Mathematical Programming, Bruxelles, May.]. Given a directed graph G, a closure of G is defined as a subset of nodes such that if a node belongs to the closure all its successors also belong to the set. If a real number is associated to each node of G a maximal closure is defined as a closure of maximal value.

Parameter identification in distributed systems: A synthesizing overview

Abstract: This paper surveys the distributed system parameter identification problem and concludes that it can be treated as a series of largely independent subproblems, each of which must be considered in any attempt to treat the problem in applications. An approach is discussed which treats in a unified manner all the inherent subproblems. An annotated bibliography of the literature in the field analyzes the contributions of the various authors to each step in the solution of problems of parameter identification in distributed systems. The applications of existing techniques are discussed, and the paper closes with conclusions and recommendations for future work in the field.

Mixing of viscoelastic fluids with helical-ribbon agitators. I — Mixing time and flow patterns

Abstract: Batch mixing of viscous fluids with helical-ribbon agitators in 2.4 liter and 13 liter vessels has been studied for agitator speeds up to 200 RPM. Seven different agitators of different dimensions were employed in this work. Mixing times were measured using a decoloration technique and circulation times were determined by the tracer bead method. In addition, velocity profiles were obtained from streak photographs using selective illumination of the vessel and PVC powder as tracer particles. It was found that the mixing times of Newtonian fluids, which agreed with previously published data, were considerably (3 to 7 times) shorter than those of the viscoelastic fluids. The mixing time was strongly affected by the fluids' elasticity; increasing as the fluid elasticity increased. The velocity profiles were qualitatively similar for all the fluids but showed decreased axial circulation and increased circumferential flow as fluid elasticity increased. However, mixing is not only a function of the axial circulation (impeller pumping rate) but also is a function of the perturbations superimposed on the main flow. A simple, first approximation model based on the impeller geometry and flow patterns is proposed to correlate the circulation capacity and mixing time data for the various geometries studied. On a etudie, en employant des vitesses d'agitation atteignant 200 tours a la minute, le melange discontinu de fluides visqueux assure par des agitateurs a ruban helicoidal dans des vaisseaux de 2.4 litres et 13 litres; on a utilise a cette fin sept agitateurs differents de dimensions variees. On a mesure les temps de melange par une methode de decoloration et determine les temps de circulation au moyen d'une methode a base de perles marquees. On a, en outre, obtenu des profils de vitesse a partir de photographies avec stries, en utilisant un eclairage selectif du vaisseau et de la poudre de chlorure de polyvinyle qui servait pour les particules marquees. On a trouve que les temps de melange des fluides newtoniens, qui correspondaient a ceux qui ont deja ete publies, etaient bien plus faibles (3 a 7 fois) que les temps de melange des fluides visco-elastiques. L'elasticite des fluides a considerablement affecte le temps de melange, qui augmentait avec celleci. Les profils de vitesse se sont averes qualitativement semblables pour tous les fluides, mais ils ont indique une circulation axiale moindre et un ecoulement circonferentiel accru, a mesure que l'elasticite des fluides augmentait. Toutefois, le melange est une fonction non seulement de la circulation axiale, (taux de pompage du rotor), mais aussi des perturbations sur-imposees sur l'ecoulement principal. On propose un modele simple et fournissant une premiere approximation, lequel est base sur la geometrie du rotor et les types d'ecoulement, en vue d'etablir des correlations entre les resultats relatifs a la circulation et aux temps de melange, dans le cas des diverses formes geometriques etudiees.

Polymer composites containing plasma‐treated mica. I. Flow and mechanical properties

Abstract: Suzorite mica has been surface modified by microwave plasma treatment in ethylene gas. The surface-treated mica was used as a filler in polyethylene, polystyrene, and a mixture of these two polymers. Significant changes in rheological behavior ensue. These indicate that adhesion between polyethylene and irradiated mica is superior to that of interfaces using unirradiated mica. In contrast, ethylene irradiation reduces the ability of filled polystyrene compounds to store elastic energy in melt flow, an effect consistent with impaired adhesion at interfaces involving these components. An intermediate situation exists in the case of the two-polymer blend. The tensile properties of these systems also reflect surface treatment, reinforcement occurring in polyethylene-containing compounds, while the tensile properties of polystyrene composites deteriorate. Plasma-induced surface modifications of fillers to produce desired property changes in specified polymer matrixes are implied by the present work, but a fuller understanding of the chemistry of surface modification reactions is needed to substantiate these implications.

Polymer composites containing plasma-treated mica. II. Dielectric properties

Abstract: The complex relative premittivity K*(ω) of polymer–mica composites has been studied in the frequency range extending from about 10−2 to 107 Hz. Microwave plasma treatment in ethylene of the mica flakes leads to significant alterations of K*(ω) for the matrix polymers used—polyethylene, polystyrene, and a mixture of these two polymers. The origins of the dispersion characteristics were investigated using a series of polyethylene samples containing up to 50 wt-% of untreated mica. Comparing experimental results with theoretical analyses of the Maxwell-Wagner-Debye-like interfacial polarization effect, it is possible to identify two major contributions to K*(ω): a Debye-like dispersion centered near 102 Hz and a charge-diffusion mechanism which contributes primarily at low frequencies (≲10 Hz).

Traps in Al2O3 detected by tunneling

Abstract: New structure, quite different from inelastic tunneling peaks, has been observed in electron tunneling spectra of MOM junctions. A capacitance peak is associated with this structure, which is attributed to traps in the oxide at energies smaller than those previously reported. The C‐V characteristics calculated using a single‐energy trap model agree with experimental results; however, no satisfactory explanation has yet been found to account for the strong temperature dependence of the trap energy levels.

Polymer Composites with Plasma-Treated Fillers

Abstract: A Large-volume Microwave Plasma (LMP) generator has been used to irradiate mica and ground-wood fibers in inert and active gas environments. Irradiated fillers were subsequently incorporated in a polypropylene matrix at solids levels of 10 and 20%. Calorimetrically measured heats of immersion showed that substantial changes in surface properties of fillers were effected by irradiation in ethylene, ammonia, and similar active gases. These surface changes are reflected In ultimate tensile and elongation properties of composites which show marked improvement over controls based on unirradiated fillers. Although no appreciable response in melt viscosity has been observed, surface treatment of fillers does seem to increase significantly melt elasticity of filled composites. The implications of improved performance motivate a more detailed study of the use potential of LMP in the fomulation of polymer composites.

Free radical formation in electrical trees in polyethylene

Abstract: It has been suggested that free radicals may be formed and that they may play a significant role in the electrical treeing process in solid polyethylene (PE).1 The techniques of electron paramagnetic resonance (EPR) should then be advantageous in a study of electrical treeing mechanisms, since EPR responds only to systems containing unpaired electrons, such as free radicals. The hyper-fine structure of the EPR spectra can provide information about the nature of these radicals. In addition, radicals of differing lifetimes, and their evolution with time may be studied by this technique.

Sensitivity Analysis in Multilinear Systems.

Abstract: The primary objective of this study is to examine tho sensitivity properties of a multilinear plant embedded in a feedback structure. As a prelude tho existing linear theory ia summarized and extended. Tho bilinear case is then treatod in detail. Extrapolation to the multilinear ease has been carried out by Porter and DeSantis (1974 a). New results includo the following : (i) the use of causality structure as a component of sensitivity analysis in closed-loop linear and non-linear systems, (ii) the establishment of terminal equivalence conditions for multilinear plants and multilinear compensators, (iii) the development of a sensitivity operator in the multilinear setting including existence conditions, (iv) extensions of linear results to largo parameter perturbations.

Property Modifications in Fibers of Blends Based on Poly(ethylene Terephthalate)

Abstract: In an effort to apply compatibility rules to the behavior of polymer fibers, tenacity of fibers spun from blends based on poly(ethylene terephthalate) has been studied. Blends containing 5% and 10% of a wide range of added thermoplastics were formulated using as a guide critical surface-tension data and solubility parameters of the components. For blends spun at 325°C a significant correlation was found between tenacity variations and differences in the compatibility parameters, suggesting that these parameters may serve as guides to the selection of compositions displaying superior fiber properties. At lower spinning temperatures melt-viscosity effects, among others, also strongly influence fiber properties. These factors, along with thermal stability effects, must be considered in attempts to optimize the tenacity of multicomponent fiber-formers.

The size of the plastic zone in general yielding fracture

Abstract: THE SIZE OF THE PLASTIC ZONE IN GENERAL YIELDING FRACTURE J. Lantei~ne, M. N. Bassim, and D. R. Hay Department of Metallurgical Engineering, Ecole Polytechnique Montreal, Quebec, Canada H3C 3A7 tel: 514/344-4771 In e v a l u a t i n g the J i n t e g r a l , a r e l a t i o n between load P and load p o i n t d i s p l a c e m e n t 6 i s o b t a i n e d [ 1 , 2 ] . An example o f such a curve i s shown in F ig . 1 f o r a compact t e n s i l e specimen o f a t o o l s t e e l (D6) cont a i n i n g a c r a c k o f l e n g t h a. Seve ra l i n v e s t i g a t o r s [3 ,4] d e s c r i b e t h i s r e l a t i o n in terms o f the p l a s t i c zone e q u a t i o n [5] as = (KZ/Oy) 2 ry ( I /an) ( i )

Variations in Dielectric Moisture Tests on Paper, Butter Fats and Grease Samples*

Abstract: Samples of materials are immersed in a liquid nitrogen bath until the sample temperature is stabilized. A dielectric moisture meter is used to measure the samples before and after the liquid nitrogen treatment. From these two measurements and a normalized calibration curve (taken from any other sample of the same material) it is possible to determine the percentage moisture content independently of the sample basis weight for given conditions.It is shown that the method can be applied to butter fats, petroleum jelly (vaseline) greases and Paper.It may also be Possible to extend this method to other materials and products.

Dielectric Measurements and Automatic Control of Materials Heated Inside Microwave Ovens

Abstract: Preliminary results obtained on an apparatus and a method for non-contact measurements on the dielectric properties of materials heated inside operating microwave ovens, are presented. Variations in the dielectric constant and the dielectric losses of a variety of materials (food, rubber, textiles, minerals, etc.) are measured inside a modified Toshiba 600 microwave oven. The temperature range of measurements varies from freezing temperatures to temperatures exceeding 1600°C. This new technique can be used to provide reliable heat controls on microwave ovens. In addition, such measurements can provide a better understanding of the dielectric-temperature dynamic processes involved when heating materials inside microwave ovens.

Nonlinear Identification in the DISCOS Position Sensor

Abstract: The electric null of the position sensor of a drag-free satellite is expected to change its location with respect to the geometrical center of the sensor due to aging. This offset creates an increasing nonlinearity in the sensor's response, causing distortion of the output signal. A technique has been developed to identify the amount of null offset from samples of the output signal only when the disturbances on the satellite are relatively constant. A linearized least squares fit is used. Difficulties are caused by parameter equivalence of first order and data noise near the center; however, accurate estimation can be obtained for large null offset.