Showing papers by "École Polytechnique de Montréal published in 1994"

Automatic signature verification: the state of the art—1989–1993

Abstract: This paper is a follow up to an article published in 1989 by R. Plamondon and G. Lorette on the state of the art in automatic signature verification and writer identification. It summarizes the activity from year 1989 to 1993 in automatic signature verification. For this purpose, we report on the different projects dealing with dynamic, static and neural network approaches. In each section, a brief description of the major investigations is given.

Effect of corona modification on the mechanical properties of polypropylene/cellulose composites

Abstract: The effect of various corona treatment conditions on the mechanical properties of cellulose fibers/polypropylene composites was studied. The cellulose fibers and polypropylene were modified using a wide range of corona treatment levels and concentrations of oxygen. The treatment level of the fibers was evaluated using the electrical conductance of their aqueous suspensions. The mechanical properties of composites obtained from different combinations of treated or untreated cellulose fibers and polypropylene were characterized by tensile stress–strain measurements; they improved substantially when either the cellulose fibers alone or both components were treated, although composites made from untreated cellulose fibers and treated polypropylene showed a relatively small improvement. The results obtained indicate that dispersive forces are mostly responsible for the enhanced adhesion. The relationship between the electrical conductance of the fibers, the mechanical properties, and the mechanism of improved adhesion is discussed. © 1994 John Wiley & Sons, Inc.

Extraction of poly-3-hydroxybutyrate using chlorinated solvents

Abstract: Recovery of poly-3-hydroxybutyrate (PHB) in three chlorinated solvents with or without acetone pretreatment and degradation of extracted PHB (99% pure) in hot chloroform were studied. When lyophilized Alcaligenes eutrophus biomass was used, the best results were obtained with acetone pretreatment and solvent reflux for 15 min in methylene chloride or chloroform. Recovered PHB had a 95% purity and molecular weights (Mw) of 1,050,000 and 930,000 g/mol respectively. Further heating resulted in a serious Mw, loss at reflux temperatures. Degradation of extracted PHB at 110°C in chloroform was due to random and chain-end scission, the former being predominant.

A Column Generation Approach to the Multiple-Depot Vehicle Scheduling Problem

Abstract: We give a new formulation to the multiple-depot vehicle scheduling problem as a set partitioning problem with side constraints, whose continuous relaxation is amenable to be solved by column generation. We show that the continuous relaxation of the set partitioning formulation provides a much tighter lower bound than the additive bound procedure previously applied to this problem. We also establish that the additive bound technique cannot provide tighter bounds than those obtained by Lagrangian decomposition, in the framework in which it has been used so far. Computational results that illustrate the robustness of the combined set partitioning-column generation approach are reported for problems four to five times larger than the largest problems that have been exactly solved in the literature. Finally, we show that the gap associated with the additive bound based on the assignment and shortest path relaxations can be arbitrarily bad in the general case, and as bad as 50% in the symmetric case.

Biomechanics of the lumbar spine in sagittal/lateral moments

Abstract: Study DesignThe nonlinear stress analysis of the antire ligamentous lumbar spine (L1-S1) in single flexion, extension, right lateral, and left lateral moments of up to 15 Nm was performed. In sagittal moments, both disc fiber angles of 27° and 30° were considered. Moreover, in extension moment, the

A γ-ray detection system for 3-D particle tracking in multiphase reactors

Abstract: A system employing eight NaI detectors has been developed for tracking particles moving in a three-phase fluidized bed reactor. One particle is tagged with typically 2 MBq of 46Sc which emits high energy γ-rays. The system is calibrated by measuring the count-rates in the 8 detectors with the tagged particle placed at a number of locations in the reactor and then calculating the count-rates, using the Monte Carlo technique, at 19 200 locations. In a tracking experiment, data are accumulated in the multiscaling mode and the coordinates of the moving particle are calculatedby least-squares using the calibration map. With 30 ms counting intervals, the location of the particle is determined with a typical precision of 5 mm. The use of these data for determining velocity flow fields in multiphase reactors is illustrated.

Path-tracking for a tractor-trailer-like robot

Abstract: Path-tracking controllers for tractor-trailer-like robots are de signed by generalizing the geometric path-tracking approach currently adopted for car-like robots. This is done by formaliz ing the concepts of speed and lateral and heading offsets and by assuming slippage-free motion. The main result is that for straight-line or circular-arc paths to be tracked with a con stant velocity, path-tracking may be ensured by means of a linear, time-invariant, and decoupled controller, the gains of which may be determined using familiar proportional-integral- derivative (PID) and state-feedback techniques.

Simulation of two-dimensional anisotropic cardiac reentry: Effects of the wavelength on the reentry characteristics

Abstract: A two-dimensional sheet model was used to study the dynamics of reentry around a zone of functional block. The sheet is a set of parallel, continuous, and uniform cables, transversely interconnected by a brick-wall arrangement of fixed resistors. In accord with experimental observations on cardiac tissue, longitudinal propagation is continuous, whereas transverse propagation exhibits discontinuous features. The width and length of the sheet are 1.5 and 5 cm, respectively, and the anisotropy ratio is fixed at approximately 4∶1. The membrane model is a mofified Beeler-Reuter formulation incorporating faster sodium current dynamics. We fixed the basic wavelength and action potential duration of the propagating impulse by dividing the time constants of the secondary inward current by an integerK. Reentry was initiated by a standard cross-shock protocol, and the rotating activity appeared as curling patterns around the point of junction (the q-point) of the activation (A) and recovery (R) fronts. The curling R front always precedes the A front and is separated from it by the excitable gap. In addition, the R front is occasionally shifted abruptly through a merging with a slow-moving triggered secondary recovery front that is dissociated from the A front and q-point. Sustained irregular reentry associated with substantial excitable gap variations was simulated with short wavelengths (K=8 andK=4). Unsustained reentry was obtained with a longer wavelength (K=2), leading to a breakup of the q-point locus and the triggering of new activation fronts.

The design of an on-line signature verification system: from theory to practice

Abstract: This paper reports on the major decisions that have to be made throughout the design phase of an automatic signature verification system It shows how knowledge about signature control and generati

Modeling of symmetric 2 × 2 fused-fiber couplers

Abstract: A complete analysis of symmetric 2 × 2 fused-fiber couplers in terms of supermode beating is made. The tranverse and longitudinal geometry of the couplers has been carefully modeled to take into account the fabrication parameters. The first two scalar supermodes and their polarization corrections have then been calculated for each degree of fusion and taper ratio, resulting in powerful tools for the design of particular couplers. The good agreement between the observed and the predicted responses for slightly and strongly fused couplers confirms the validity of each step of this analysis.

A new built-in self-test approach for digital-to-analog and analog-to-digital converters

Abstract: This paper proposes a test approach and circuitry suitable for built-in self-test (BIST) of digital-to-analog (D/A) and analog-to-digital (A/D) converters. Offset, gain, linearity and differential linearity errors are tested without using test equipment. The proposed BIST structure decreases the test cost and test time. The BIST circuitry has been designed to D/A and A/D converters using CMOS 1.2 mm technology. By only a minor modification the test structure would be able to localize the fail situation. The small value of area overhead (AOH), the simplicity and efficiency of the proposed BIST architecture seem to be promising for manufacturing.

A study of solid behavior in spouted beds using 3‐D particle tracking

Abstract: A non-invasive γ-ray emission system, employing eight NaI detectors, has been developed to follow the motion of a single radioactive particle in a three-dimensional spouted bed reactor. The count-rates measured simultaneously by the detectors are converted into tracer coordinates (x, y, z) using a pre-established calibration model which accounts for every physical and geometrical aspects involved in the spouting facility. Typically four hundred thousands successive coordinates, obtained over 3.5 hours of particle tracking, are used for determining the average particle velocity field and other hydrodynamic quantities such as the cycle time distribution, the spout shape and the solid exchange distribution at the spout boundary, which could not be evaluated accurately using any available techniques. Une methodologie nucleaire non-intrusive, employant huit detecteurs a scintillation, a ete mise au point pour l'etude de la circulation du solide dans les lits a jet tridimensionnels par la poursuite d'une particule radioactive. Les comptages de photons mesures simultanement par les detecteurs sont convertis en coordonnees cartesiennes (x, y, z) avec un modele preetabli de calibration qui decrit les interactions des photons avec les detecteurs et le reacteur. Apres avoir accumule typiquement quatre cent mille coordonnees successives sur une periode de 3.5 heures, ces donnees sont utilisees pour quantifier une variete de proprietes hydrodynamiques du solide jusque la inaccessible non-intrusivement. Cet article presente les resultats preliminaires obtenus sur le champ moyen de vitesse du solide, les distributions des temps de circulation des particules et d'echange du solide a la paroi du jet et la morphologie du jet.

Word-level training of a handwritten word recognizer based on convolutional neural networks

Abstract: We introduce a new approach for online recognition of handwritten words written in unconstrained mixed style. Words are represented by low resolution "annotated images" where each pixel contains information about trajectory direction and curvature. The recognizer is a convolutional network which can be spatially replicated. From the network output, a hidden Markov model produces word scores. The entire system is globally trained to minimize word-level errors.

Critical evaluation and optimization of the thermodynamic properties and phase diagrams of the Al-Mg, Al-Sr, Mg-Sr, and Al-Mg-Sr systems

Abstract: All available thermodynamic and phase diagram data were critically assessed for all phases in the Al-Mg, Al-Sr, and Mg-Sr systems at 1 bar pressure from room temperature to above the liquidus temperatures. For these systems, all reliable data were simultaneously optimized to obtain a set of model equations for the Gibbs energy of the liquid alloy and all solid phases as functions of composition and temperature. The modified quasi-chemical model was used for the liquid. The Al-Mg-Sr ternary phase diagram was calculated from the optimized thermodynamic properties of the binary systems. Since no reliable ternary data were available, three assumptions were made: no ternary terms were added to the model parameters for the thermodynamic properties of the liquid, no ternary solid solutions are present in the system, and no ternary compound is present in the system. The calculated ternary phase diagram is thus a first approximation, which can be improved by the addition of new experimental data and can be used as a base for the calculation of phase diagrams of multicomponent systems.

Structural and magnetic characterization of granular Y1Ba2Cu3O7−δ nanocrystalline powders

Abstract: High energy ball milling has been used to produce nanocrystalline Y1Ba2Cu3O7-δ powders. These powders are being used as starting materials for manufacturing superconducting textured wires by a solid state recrystallization process. Magnetic and microstructural characterizations were performed as a function of milling time. The milling reduces the average crystal size and creates low and high-angle grain boundaries which increase the granularity of the superconductor. As a result, the long-range order on the oxygen sublattice and on the yttrium and barium sites is destroyed. A transition from orthorhombic to tetragonal and finally to a cubic metastable phase is observed. Total loss of superconductivity occurs after about 1 h of milling. Prior to this time, superconductivity can partially be restored by room-temperature aging. High-temperature heat treatment of the nanocrystalline phase produces a tetragonal structure with c = 3a.

Spine layout design

Abstract: We present a method for designing spine layouts. A spine layout is a layout in which a main aisle is used for the movements between the work cells located on both side and for the temporary storage of work in process. Our objective is to find a layout that minimizes both the handling costs and the investment costs. Also, a rectangular layout shape is searched for. With the proposed method, a design skeleton is first constructed with a heuristic. This design skeleton is then optimally transposed into a net layout via an integer linear program. Numerical results for layouts of 12 and 22 cells are presented.

The optimization and application of two direct viable count methods for bacteria in distributed drinking water

Abstract: The optimal incubation conditions for the direct viable count method with nalidixic acid were determined. They do not differ from those proposed in the literature for a laboratory strain and a mixed bacterial population isolated from drinking water. The direct viable count method with 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) was performed under in situ conditions. The bacteria were incubated with CTC at a concentration of 1 mM for 4–6 h at the temperature of the water in the pipes and without the addition of an exogenous substrate. The results obtained for a laboratory strain using the two direct count methods were similar. However, for a mixed bacterial population, the counts were always higher with the CTC method than with the nalidixic acid method.Key words: drinking water, CTC, nalidixic acid, direct viable count.

The dynamics of sustained reentry in a ring model of cardiac tissue.

Abstract: This paper describes the dynamics of circus movement around a fixed obstacle, using a one-dimensional continuous and uniform ring model of cardiac tissue to simulate sustained reentry. The membrane ionic current is simulated by a modified Beeler-Reuter formulation in which the kinetics of the fast sodium current were updated using more recent voltageclamp data. Changes in the ring length are used to modify the dynamics of reentry. Reentry is stable if the ring length (X) exceeds a critical value (X crit) and complete block occurs ifX is below a minimum (X min). Irregular sustained reentry is observed at intermediate ring lengths, as a narrow range of aperiodic reentry nearX crit, and a larger range of quasi-periodic reentry at shorter ring lengths. The basic pattern of irregular reentry is an alternation between long and short cycle length, action potential duration (APD), diastolic interval (DIA), wavelength, and excitable gap. In aperiodic reentry cycle length variations are small,APD andDIA fluctuations are of medium amplitude, and conduction velocity over the whole pathway is essentially constant during successive turns. Much larger fluctuations in these various quantities occur during quasi-periodic reentry, and they increase in size asX approachesX min. The complexity of quasiperiodic reentry patterns is related to three factors: the slope of theAPD versus DIA relation, which is greater than 1, the existence of a zone of slow conduction on the ring when the excitable gap becomes quite short, and the occurrence of triggered waves of secondary repolarization and excitability recovery. In the present model, quasi-periodic reentry with triggered secondary recovery covers most of the range of ring lengths, giving rise to sustained irregular reentry. There is very close agreement between our simulation results and experimental data obtained on rings of cardiac tissue.

Analysis of role of bone compliance on mechanics of a lumbar motion segment.

Abstract: A large deformation elasto-static finite element formulation is developed and used for the determination of the role of bone compliance in mechanics of a lumbar motion segment. This is done by simulating each vertebra as a deformable body with realistic material properties, as a deformable body with stiffer or softer mechanical properties, as a single rigid body, or finally as two rigid bodies attached by deformable beams. The single loadings of axial compression, flexion moment, extension moment, and axial torque are considered. The results indicate the marked effect of alteration in bone material properties on biomechanics of lumbar segments specially under larger loads. The biomechanical studies of the lumbar spine should, therefore, be performed and evaluated in the light of such dependency. A model for bony vertebrae is finally proposed that preserves both the accuracy and the cost-efficiency in nonlinear finite element analyses of spinal multi-motion segment systems.