Showing papers by "École Polytechnique de Montréal published in 1988"
TL;DR: An efficient generalized permanent labelling algorithm is presented based on the definition of the concept of a generalized bucket and on a specific order of handling the labels to solve the shortest path problem with time windows.
Abstract: The shortest path problem with time windows (SPPTW) consists of finding the least cost route between a source and a sink in a network G = (N, A) while respecting specified time windows [ai, bi] at each visited node The duration dij of each arc is restricted to positive values while the cost Cij of each arc (i, j) Є A is unrestrictedThis article presents an efficient generalized permanent labelling algorithm to solve this problem This new algorithm is based on the definition of the concept of a generalized bucket and on a specific order of handling the labels The algorithm runs in pseudo-polynomial time Problems with up to 2500 nodes and 250,000 arcs have heen solved
369 citations
TL;DR: It was found that the long-term success of alumina-alumina total hip replacement depends on both the ceramic microstructure (small grain size with uniform distribution, minimum porosity, absence of inclusions) and implant geometry (sphericity deviation +/- 1 micron, radius tolerance between components 7-10 microns).
Abstract: The purpose of this article was to review the laboratory and clinical performances since 1970 of a total hip prosthesis using alumina–alumina combination. The chemical and physical properties of dense alumina ceramic were studied in relation to biocompatibility, mechanical strength, and surface properties. Through the examination of 35 retrieved implants, it was found that the long-term success of alumina–alumina total hip replacement depends on both the ceramic microstructure (small grain size with uniform distribution, minimum porosity, absence of inclusions) and implant geometry (sphericity deviation ±1 μm, radius tolerance between components 7–10 μm). Alumina component wear and fractures have disappeared with the use of high-performance materials and severe manufacturing quality control. Examination of human biopsies from well-fixed prostheses showed that alumina particles deposits increase with time with only a low-grade macrophagic reaction. When loosening occurred, an inflammatory reaction appeared; this reaction was less striking than with loose metal–polyethylene prostheses, however. The long-term behavior of cementless alumina cup fixation depends upon initial positioning and stability; survivorship analysis of the cemented ceramic cups showed an 88% survival probability after 8 years with a 1.6% average annual probability of revision. The percentage of surviving was 100% after 8 years in patients who were less than 50 years old. Aseptic loosenings occurring at the cup–cement interface were assumed to be related to stress protection secondary to the high rigidity of the ceramic leading to a weakening of the spongious bone supporting the cement mantle. Good bone stock quality as well as high-quality ceramic appear to be the prerequisites for durable fixation of alumina sockets.
284 citations
TL;DR: The most striking deviations from configurational randomness were observed at low nitrogen contents where more than two out of three silicon neighbors of a given nitrogen atom are monohydrogenated.
Abstract: The composition of hydrogenated silicon nitride films produced either by plasma-enhanced chemical-vapor deposition (PECVD) with 0.01\ensuremath{\le}[${\mathrm{NH}}_{3}$]/[${\mathrm{SiH}}_{4}$]\ensuremath{\le}20 in the 220--320-\ifmmode^\circ\else\textdegree\fi{}C temperature range or by low-pressure chemical-vapor deposition at 800 \ifmmode^\circ\else\textdegree\fi{}C was determined by elastic-recoil-detection techniques and compared with the relative and absolute atomic densities deduced from x-ray photoelectron spectroscopy and optical measurements in the infrared (ir) range. The [N]/[Si] ratio of PECVD samples followed a square-root dependence on [${\mathrm{NH}}_{3}$]/[${\mathrm{SiH}}_{4}$] over most of the gas-ratio range. We propose original calibrations of most of the ir-absorption bands observed in these samples over the 600--3600-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ range, and we derived the experimental bond statistics by assuming complete valence satisfaction. In particular, the oscillator-strength factor of each of the six components of the SiH stretching peak was determined. The detailed statistics of all the hydrogenated configurations established for the first time in such a silicon-based ternary alloy are then compared to those expected to those expected for a random-bonded network. The most striking deviations from configurational randomness were observed at low nitrogen contents where more than two out of three silicon neighbors of a given nitrogen atom are monohydrogenated. Nitrogen atoms are found to have at least one monohydrogenated silicon nearest neighbor in all samples up to [N]/[Si]=1.1. The generality of such a second-neighbor correlation in hydrogenated III-IV amorphous alloys is also discussed.
279 citations
TL;DR: In this article, the state-of-the-art in double-multiple streamtube method for modeling the Darrieus-type vertical-axis wind turbine (VAWT) is described.
Abstract: This work describes the present state-of-the-art in double-multiple streamtube method for modeling the Darrieus-type vertical-axis wind turbine (VAWT) Comparisons of the analytical results with the other predictions and available experimental data show a good agreement This method, which incorporates dynamic-stall and secondary effects, can be used for generating a suitable aerodynamic-load model for structural design analysis of the Darrieus rotor 32 references
165 citations
TL;DR: A stereoradiographic method was developed to measure the three-dimensional shape of the rib cage in vivo in order to provide descriptive data and to study symmetry in the normal population, although a trend of inequality of rib angulation at all anatomical levels was observed.
129 citations
TL;DR: The feasibility of the hydrogenation of toluene into methylcyclohexane over a Ni/SiO 2 aerogel catalyst in a flow fixed bed reactor has been demonstrated in the temperature range 90 to 150°C as mentioned in this paper.
68 citations
TL;DR: In this paper, the hamiltonian structure of the time evolution of incompressible elastic fluids was shown to possess the same properties as that of the Hamiltonian structure. But this is not the case for all elastic fluids.
64 citations
TL;DR: In this article, a dual effort was undertaken to provide the needed data: (1) thermodynamic phase diagram analysis and calculation of the ternary solidus and liquidus surfaces and (2) experimental determination of liquidus temper- atures for selected alloys.
58 citations
TL;DR: In this article, a thermodynamic database for molten salt solutions is developed through the systematic optimization of binary and ternary data, and a sublattice model is used for calculating activities in multicomponent solutions.
Abstract: A thermodynamic database for molten salt solutions is being developed through the systematic optimization of binary and ternary data. Over 200 systems have been evaluated. Parameters for the subsystems of the Li, Na, K/F, Cl, OH, CO3, SO4 system are tabulated. For calculating activities in multicomponent solutions, a sublattice model is used. Equations for integral and partial properties are given in full. For each sublattice it is shown how a consistent “Kohler -Toop” (or “Muggianu-Toop”) formalism can be devised for multi component systems. The practical significance and importance of the various terms in the sublattice model as applied to molten salts are discussed. An example of automatic accessing of the multicomponent salt database for equilibrium calculations with the F∗A∗C∗T system is presented.
47 citations
TL;DR: In this article, the authors considered a vehicle routing problem with full loads and time limit constraints and formulated it as an asymmetrical traveling salesman problem with two types of restrictions, and showed that the problem can be solved optimally for relatively large sizes.
44 citations
TL;DR: The extent score, an index of active progressive disease, is an independent predictor of mortality and cardiac events in patients with coronary artery disease.
Abstract: The clinical and angiographic correlates and the prognostic significance of the “coronary extent score” in a consecutive series of 313 patients who were catheterized twice were studied. The extent score was defined as the number of 5 to 75% stenosed segments in a 15-segment coding system. The extent score was higher in subgroups of patients with new onset angina at the time of the first angiogram (4.3 ± 2.4 vs 3.3 ± 1.9, p
TL;DR: In this paper, an on-line estimation of the specific growth rate in a fermentation process in the case when a soluble product is measured on online is presented. But the authors do not consider the effect of the filtering effect on specific growth rates.
Abstract: This paper deals with the on-line estimation of the specific growth rate in a fermentation process in the case when a soluble product is measured on-line. The proposed algorithm belongs to a larger class of on-line estimation algorithms which present the following advantages: they do not require any analytical expressions for the specific growth rate; their theoretical stability and convergence have been emphasized; since their structure includes a filtering effect, the estimation results exhibit less erratic values for the specific growth rate than when obtained by direct calculation from the biomass concentration equation. Real-life results on an ethanol producing process are presented. Finally. it is shown how estimation results can be used for modelling purposes.
Nous nous sommes interesses dans cet article a l'estimation en ligne de la vitesse specifique de croissance dans un procede de fermentation lorsque un produit soluble est mesure en ligne. L'algorithme propose fait partie d'une categorie plus large d'algorithmes d'estimation en ligne qui presentent les avantages les suivants: ils ne necessitent aucune expression analytique pour la vitesse specifique de croissance; leur stabilite et leur convergence theoriques ont ete amplifiees; leur structure incluant un effet filtrant, les resultats d'estimation affichent des valeurs plus regulieres pour la vitesse speifique de croissance que celles obtenues par calcul direct a partir de l'equation de concentration de biomasse. On presente des resultats d'estimation obtenus dans un procede de production d'ethanol. Enfin, on montre comment utiliser les resultats d'estimation a des fins de modelisation.
TL;DR: In this paper, a cyclic diffusion process was used to construct aggregate load models for a portion of power system loads controlled by thermostat (heating or cooling loads), following an approach inspired from the methods of statistical mechanics.
Abstract: A cyclic diffusion process—a member of the class of hybrid-state Markov processes—has been used to construct aggregate load models for a portion of power system loads controlled by thermostat (heating or cooling loads), following an approach inspired from the methods of statistical mechanics. The statistical properties of the process are analysed using renewal theory and the Fokker–Planck equation.
TL;DR: In this article, the phase analysis in Fourier transform infrared photoacoustic spectroscopy with the detection of sorbed water in polyethylene has been demonstrated for depth localization of absorbing species within the thermal diffusion length.
Abstract: Fourier transform infrared photoacoustic spectroscopy is greatly improved by the simultaneous measurement of the photoacoustic signal amplitude and phase. Saturation effects, sample dilation, and optical scattering, even in heterogeneous samples, can be easily corrected to give the absorption coefficient real value. Quantitative analyses without any special sample preparation or special photoacoustic cell are now possible. Moreover, the phase of the photoacoustic signal permits depth localization of the absorbing species within the thermal diffusion length. Surface analyses are thus possible that have a depth resolution at least one order of magnitude higher than that obtained by changing the thermal diffusion length. In this paper we illustrate the advantages of phase analysis in Fourier transform infrared photoacoustic spectroscopy with the detection of sorbed water in polyethylene.
TL;DR: In this paper, a least-squares optimization technique is presented which enables the parameters of the model for binary solutions to be calculated by simultaneous analysis of all experimental thermodynamic and phase diagram data.
Abstract: In previous articles the authors have presented a modification of the quasichemical theory for short range order which permits one to represent the thermodynamic properties of ordered liquid solutions such as molten silicates. In the present article, a least-squares optimization technique is presented which enables the parameters of the model for binary solutions to be calculated by simultaneous analysis of all experimental thermodynamic and phase diagram data. The MnO-SiO 2 system is used as an example. Only 3 parameters are required to represent all available data for this system.
TL;DR: In this article, a chemithermomechanical pulp of hard wood (aspen) fibers having selected aspect ratio (length/diameter) was first encapsulated with polystyrene and then mixed with poly styrene polymer at various concentrations.
Abstract: Cellulose fibers are selected as a reinforced filler for thermoplastics due to their superior mechanical properties and lower price compared to the thermoplastics. In the present study chemithermomechanical pulp of hard wood (aspen) fibers having selected aspect ratio (length/diameter) were first encapsulated with polystyrene and then mixed with polystyrene polymer at various concentrations.Mechanical properties were measured on compression molded samples containing between 10 and 40 weight percent of cellulose fibers. Experimental results show a signifi cant increase in tensile stress and modulus with fiber concentration. Using the constituent properties, an efficiency factor of stress transfer between fiber and polymer matrix was calculated and was shown to be constant for the various fiber concentrations. Theoretical predictions of tensile stress and modulus using the basic composite theory have been made. Large differences between experimental results and theoretical predictions have been observed and...
TL;DR: In this article, the assignment of airplanes to terminal gates should take into account not only the physical constraints of the terminal, but also the incoveniences suffered by the transporter and the travellers when a craft has to be serviced away from the terminal.
TL;DR: In this article, the authors investigated the effect of operating parameters such as pressure, etchant gas composition, excitation frequency and sample temperature upon etch kinetics, and observed distinct maxima in the etch rate as functions of pressure and CF4 concentration.
Abstract: We have investigated O2/CF4 plasma etching of five commercial polymers: polyimide, polyamide, polyethylene terephthalate, polycarbonate and cured epoxy resin. A new large-area microwave plasma apparatus has been used in this work, but the same apparatus can also be used as a capacitively coupled radiofrequency (13.56 MHz) discharge reactor. The effect of operating parameters such as pressure, etchant gas composition, excitation frequency and sample temperature upon etch kinetics has been examined. We have observed distinct maxima in the etch rate as functions of pressure and CF4 concentration. Activation, energies evaluated from the Arrhenius plots fall in the range 0.04-0.2 eV, in agreement with data in the literature. Dry etch susceptibility of a given polymer correlates strongly with the degree of unsaturation in the polymer's structure
TL;DR: In the presence of axial compression with and without sagittal shear force, flexion considerably increases the intradiscal pressure while extension reduces it, and disk pressure is predicted to be noticeably larger in flexion than in extension.
Abstract: A 3-D nonlinear mathematical model is used to analyze the mechanical response of a lumbar L2-3 motion segment including the posterior elements when subjected to combined sagittal plane loads. The loadings consist of axial compression force, anterior and posterior shear forces, and flexion and extension moments. The facet articulation is modelled as a general moving contact problem and the ligaments as a collection of uniaxial elements. The disk nucleus is considered as an inviscid fluid and the annulus as a composite of collagenous fibers embedded in a matrix of ground substance. The presence of axial compression force reduces the segmental stiffness in flexion whereas a reverse trend is predicted in extension. In the presence of axial compression with and without sagittal shear force, flexion considerably increases the intradiscal pressure while extension reduces it. In other words, under an identical compression force, disk pressure is predicted to be noticeably larger in flexion than in extension. The segmental mechanical response in extension loadings is markedly influenced by the changes in the relative geometry of the articular surfaces at the lower regions. Finally, the deformation of the bony structures plays a significant role in the segmental mechanics under relatively large loads.
01 Jul 1988
TL;DR: In this article, the effect of long term rock deformation on lining pressure is considered using different concepts of rock behaviour, such as linear-viscoelastic, linear-elastic linear viscous, and linear elastic non-linear viscous rock behaviour.
Abstract: The effect of long term rock deformation on lining pressure is considered using different concepts of rock behaviour. These include the conventional characteristic-line or convergence-confinement method, modified to allow for rock ageing, and lining-rock interaction methods using models of linear-viscoelastic, linear-elastic linear viscous, and linear elastic non-linear viscous rock behaviour. Calculations of lining pressures show that the former tends to underestimate, compared with the latter.
TL;DR: It is shown how this theory permits the modeling of production and preventive maintenance scheduling in a flexible manufacturing system through a set of optimality conditions derived.
Abstract: One considers a class of systems described by a set of state equations indexed over a finite set E. A random jump process with value in E represents the perturbations affecting the system. We assume that this process is a Markov chain whose transition rates depend on the system state and control. A state discontinuity is triggered by any jump of the perturbation process. A discounted expected cost accumulated over an infinite time horizon is to be minimized. A set of optimality conditions are derived for this problem. It is shown how this theory permits the modeling of production and preventive maintenance scheduling in a flexible manufacturing system.
TL;DR: In this article, the authors compare two dynamic-stall methods and experimental data for a 17-m Sandia wind turbine and conclude that the Gormont model provides a good prediction of the dynamic stall regime, characterized by a plateau oscillating near the experimental data of rotor power vs wind speed at the equator.
Abstract: Comparisons have been made between aerodynamic performance predictions using two dynamic-stall methods and experimental data for a 17-m Sandia wind turbine. These dynamic-stall models are the incidence delay methods originating from Boeing-Vertol and from the Massachusetts Institute of Technology, which are based on numerical correlations of the dynamic-stall delay with pitch rate parameter. The MIT model calculations show that aerodynamic coefficients are underestimated in comparison with those of the Gormont model, even if the shape of the curves is quite the same. The MIT model provides a good prediction of the dynamic-stall regime. This is characterized by a plateau oscillating near the experimental data of the rotor power vs wind speed at the equator
TL;DR: In this article, the mechanical and rheological properties of high density polyethylene filled with carbon black have been examined, and the relationship between the yield stresses, filler percentage, surface modification by the coupling agents and mechanical properties is discussed.
Abstract: The mechanical and rheological properties of high density polyethylene filled with carbon black have been examined. Two sources of carbon black (one commercial and other obtained from a pyrolysis process) and various treatments have been studied. The rheological measurements in the melt state has been performed on a Rheometrics stress rheometer and a capillary rheometer. These materials possess outstanding hardness and toughness showing great potential for structural application. Comparison of carbon black from two sources showed that the carbon from the pyrolysis process has a good potential as a reinforcing agent. It was found that surface treatment reduces the particle-particle interactions and improves the filler dispersion. The relationship between the yield stresses, filler percentage, surface modification by the coupling agents and mechanical properties is discussed.
TL;DR: A variation on Peterson's modification of the Lowry method for microbial protein determination was developed in which 10% oxalic acid was used to remove jarosite, which allowed the quantification of Thiobacillus ferrooxidans entrapped in solid jarosite or in aqueous suspensions containing jarosite.
Abstract: A variation on Peterson's modification of the Lowry method for microbial protein determination was developed in which 10% (w/v) oxalic acid was used to remove jarosite. This allowed the quantification of Thiobacillus ferrooxidans entrapped in solid jarosite or in aqueous suspensions containing jarosite. The quantity of protein measured was not affected by the amount of jarosite in the culture, the concentration of oxalic acid, or the time of exposure (up to 72 h) of the sample to oxalic acid. An application of this method was demonstrated in the quantification of biomass immobilized in jarosite on the surface of polystyrene beads in an inverse fluidized bed bioreactor used for the rapid microbial oxidation of ferrous iron.
TL;DR: In this paper, the effects of plasma etching on surface structure and chemistry of several papers have been investigated; the thermal activation energy determined from the latter was found to be 0.15 eV.
Abstract: The effects of plasma etching on surface structure and chemistry of several papers have been investigated. Plasma etching acts like a fine microtome, continuously removing infinitesimally thin layers at the surface. It has allowed us to observe the internal structure of fibers, and interfiber bonding. The kinetics of plasma etching and its temperature dependence are reported; the thermal activation energy determined from the latter was found to be 0.15 eV. Possible applications of plasma etching techniques to study the structural and physical properites of paper in the z-direction and the distribution of coating material across the thickness of a paper sample are discussed.
01 Jul 1988
TL;DR: A two-level algorithm is proposed, which yields a suboptimal solution through a sequence of linear programming problems, but the optimality of solutions produced with the approach is established in the cases of one cycle and for steady-state operations.
Abstract: This paper presents a model for the optimization of productivity in a steel plant comprised of four arc furnaces and three continuous casting machines and subject to a global limitation on the power supplied to the furnaces. The furnaces produce in batch mode and require a given amount of energy at each fusion phase in a production cycle. The problem is to define the starting time and duration of each phase for each production cycle, in combination with a power schedule which meets the energy requirements of the different furnaces and a global power supply limit for the whole plant, in order to minimize the due date of the last production cycle. This scheduling problem is formulated as a nonstandard optimization problem, combining an optimal control problem and a mathematical programming problem. A two-level algorithm is proposed, which yields a suboptimal solution through a sequence of linear programming problems. The optimality of solutions produced with the approach is established in the cases of one cycle and for steady-state operations.
TL;DR: In this paper, the microwave drying of 13X zeolite is experimentally studied by continuously measuring the permittivity of a sample material during given microwave drying cycles, showing that the adsorbed water molecules are much less mobile than the free water molecules.
Abstract: The microwave drying of 13X zeolite is experimentally studied by continuously measuring the permittivity of a sample zeolite material during given microwave drying cycles. The results are interpreted in light of the dielectric theory of heterogeneous mixtures, making it possible to distinguish the water vapor in circulation within the zeolite structure from the water absorbed on the solid material. The results agree with previous data, showing that the adsorbed water molecules are much less mobile than the free water molecules. Time constants involved with the desorption and transport processes of water are obtained under microwave power heating conditions. >
TL;DR: In this article, the equivalence between trend surface analysis with polynomials of orderk and IRF-k kriging with a nugget effect covariance model was established.
Abstract: This short note establishes the equivalence between trend surface analysis with polynomials of orderk and IRF-k (intrinsic random function of orderk) kriging with a nugget effect covariance model.
TL;DR: In this article, the fatigue propagation rates and fatigue threshold ( ΔKth) values on copper and 70-30 α-brass of two different grain sizes in laboratory air and dry argon were studied (R = 0.1 and frequency = 20 Hz).
Abstract: The fatigue propagation rates and fatigue threshold ( ΔKth) values were studied (R = 0.1 and frequency = 20 Hz) on copper and 70-30 α-brass of two different grain sizes in laboratory air and dry argon. With decreasing grain size, the threshold increased in copper, while it decreased in α-brass. These results suggest that in copper, crack tip plasticity considerations were more important in determining the threshold values than crack closure effects. Dry argon increased ΔKth slightly in copper and more significantly in α-brass. A transition from completely transgranular to partially intergranular and back to completely transgranular cracking was observed with decreasing crack growth rates in both materials and environments. The growth rates for which intergranular cracking was obtained were found to be consistent with a hydrogen embrittlement mechanism, associated with adsorption of water molecules and dislocation transport of hydrogen.
TL;DR: In this article, a mathematical model based on diffusion-convection equations is used to describe the rheological properties of dilute polymer solutions, using a second-order conformation tensor as a measure of the internal strain; this model uses a more detailed description of the macromolecules and also avoids the necessity of introducing additional ad-hoc assumptions (closure approximations) commonly used in other molecular theories.
Abstract: A mathematical model based on the diffusion-convection equations is used to describe the rheological properties of dilute polymer solutions. The model uses a second-order conformation tensor as a measure of the internal strain; this avoids the mathematical complexity resulting from the use of a more detailed description of the macromolecules and also avoids the necessity of introducing additional ad-hoc assumptions (closure approximations) commonly used in other molecular theories. The rheological equation is obtained in terms of the rate-of-deformation tensor\(\dot \gamma \) and a scalar functionf(σ) relating the extra stress tensorσ to the internal strain tensorc. The functionf(σ) depends on the physical insight introduced in the Helmholtz free energyA(c) of the solvent-polymer system.