Showing papers by "École Polytechnique de Montréal published in 2000"

Customer‐perceived value in industrial contexts

Abstract: Although customer‐perceived value is discussed widely in the literature, few empirical studies have been conducted due to an absence of operational measures. Reports on the development of measures and tests two customer‐perceived value structures using data collected from industrial customers of the information technology industry. The findings generally support both structures and provide empirical support for a value proposition with 13 value drivers. Furthermore, results indicate that most of the 13 drivers are assessed in a similar way by industrial customers of three service sectors surveyed, ICE (information, communication, entertainment), distribution and finance. Flexibility and responsiveness – two service‐related benefits – are important value drivers for all the business customers surveyed. Relationship value drivers are assessed the most differently in two of the three sectors studied, finance and ICE (information, communication, entertainment).

The Modified Quasichemical Model I— Binary Solutions

Abstract: Further improvements to the modified quasichemical model in the pair approximation for short-range ordering in liquid and solid solutions are presented. The energy of pair formation is expanded in terms of the pair fractions rather than the component fractions, and coordination numbers are permitted to vary with composition. A formalism is introduced whereby the quasichemical equations are shown to be equivalent to the equations of an associate model if the pairs are formally treated as fractional associates. The model is applied to the liquid phase in a new optimization of the KCl-MgCl2 system.

The potential of distributed generation to provide ancillary services

Abstract: The growing concerns regarding electric power quality and availability have led to the installation of more and more distributed generation. In parallel and in the context of an accelerating trend towards deregulation of the electric industry, the unbundling of services, many grouped under ancillary services, should create a market for some of these services. This paper discusses the potential of distributed generation (DG) to provide some of these services. In particular, DG can serve locally as the equivalent of a spinning reserve and voltage support of the AC bus. The main types of distributed generation with emphasis on the power electronic interface and the configurations appropriate to provide ancillary services are reviewed. The flexibility and features provided by the power electronic interface are illustrated. In addition to control of the real power, other functions can be incorporated into the design of the interface to provide services, such as reactive power, and resources associated with power quality. These include voltage sag compensation and harmonic filtering. The implications on the design of the power converter interface are discussed.

A branch and cut algorithm for nonconvex quadratically constrained quadratic programming

Abstract: We present a branch and cut algorithm that yields in finite time, a globally e-optimal solution (with respect to feasibility and optimality) of the nonconvex quadratically constrained quadratic programming problem. The idea is to estimate all quadratic terms by successive linearizations within a branching tree using Reformulation-Linearization Techniques (RLT). To do so, four classes of linearizations (cuts), depending on one to three parameters, are detailed. For each class, we show how to select the best member with respect to a precise criterion. The cuts introduced at any node of the tree are valid in the whole tree, and not only within the subtree rooted at that node. In order to enhance the computational speed, the structure created at any node of the tree is flexible enough to be used at other nodes. Computational results are reported that include standard test problems taken from the literature. Some of these problems are solved for the first time with a proof of global optimality.

Training hidden Markov models with multiple observations-a combinatorial method

Abstract: Hidden Markov models (HMM) are stochastic models capable of statistical learning and classification. They have been applied in speech recognition and handwriting recognition because of their great adaptability and versatility in handling sequential signals. On the other hand, as these models have a complex structure and also because the involved data sets usually contain uncertainty, it is difficult to analyze the multiple observation training problem without certain assumptions. For many years researchers have used the training equations of Levinson (1983) in speech and handwriting applications, simply assuming that all observations are independent of each other. This paper presents a formal treatment of HMM multiple observation training without imposing the above assumption. In this treatment, the multiple observation probability is expressed as a combination of individual observation probabilities without losing generality. This combinatorial method gives one more freedom in making different dependence-independence assumptions. By generalizing Baum's auxiliary function into this framework and building up an associated objective function using the Lagrange multiplier method, it is proven that the derived training equations guarantee the maximization of the objective function. Furthermore, we show that Levinson's training equations can be easily derived as a special case in this treatment.

Measuring and characterizing system behavior using kernel-level event logging

Abstract: Analyzing the dynamic behavior and performance of complex software systems is diffcult. Currently available systems either analyze each process in isolation, only provide system level cumulative statistics, or provide a fixed and limited number of process group related statistics. The Linux Trace Toolkit (LTT) introduced here provides a novel, modular, and extensible way of recording and analyzing complete system behavior. Because all significant system events are recorded, it is possible to analyze any desired subset of the running processes, and for instance distinguish between the time spent waiting for some relevant event (data from disk or another process) versus time spent waiting for some unrelated process to use up its time slice. Despite the extensive information gathered, experimental results show that the LTT time and memory overhead is minimal (< 2:5% when observing core kernel events). Moreover, due to the LTT and Linux kernel modularity and open source code availability, the system is easily extended both in terms of system events gathered, and of later post-processing and graphical presentation.

The Chondrocyte Cytoskeleton in Mature Articular Cartilage: Structure and Distribution of Actin, Tubulin, and Vimentin Filaments

Abstract: We investigated the structure of the chondrocyte cytoskeleton in intact tissue sections of mature bovine articular cartilage using confocal fluorescence microscopy complemented by protein extraction and immunoblotting analysis. Actin microfilaments were present inside the cell membrane as a predominantly cortical structure. Vimentin and tubulin spanned the cytoplasm from cell to nuclear membrane, the vimentin network appearing finer compared to tubulin. These cytoskeletal structures were present in chondrocytes from all depth zones of the articular cartilage. However, staining intensity varied from zone to zone, usually showing more intense staining for the filament systems at the articular surface compared to the deeper zones. These results obtained on fluorescently labeled sections were also corroborated by protein contents extracted and observed by immunoblotting. The observed cytoskeletal structures are compatible with some of the proposed cellular functions of these systems and support possible microenvironmental regulation of the cytoskeleton, including that due to physical forces from load-bearing, which are known to vary through the depth layers of articular cartilage.

Sterilization by Low-Pressure Plasma: The Role of Vacuum-Ultraviolet Radiation

Abstract: Low-pressure plasma is a promising method for destroying microorganisms, an alternative to “conventional” methods, which have numerous drawbacks. Several plasma-based sterilization technologies are presently under development, even though the exact role of the various plasma constituents, for example ultraviolet radiation, on the sterilization mechanism is still unknown and subject to controversy. In this study, we first report high sporicidal activity of a microwave (MW) plasma compared to its radio-frequency (RF) counterpart, which we believe to be due to the higher concentration of reactive particles in the former plasma. We then report a relatively low sporicidal efficacy of vacuum ultraviolet (VUV) radiation (between 115 and 170 nm) emitted by an hydrogen MW plasma, in spite of the high effectiveness of these photons to break chemical bonds. We discuss these results in terms of etching (ablation), which we have observed for both synthetic polymers and spores, and in terms of other possible mechanisms proposed in the literature. The sporicidal effectiveness of VUV/UV radiation appears to vary markedly with wavelength and intensity, on account of spore structure and molecular absorption.

Control of the Subinclusion Microstructure in HDPE/PS/PMMA Ternary Blends

Abstract: Various ternary blends of HDPE, PS, and PMMA were prepared in one step using a Brabender mixer. When HDPE is the major component, as in this case, the morphology consists of a HDPE matrix, a PS dispersed phase and PMMA subinclusions within the dispersed PS, as predicted by the spreading coefficients. SEM observation and quantitative characterization were used to show that this complex morphology occurs within the first minutes of mixing and remains stable thereafter. Furthermore, it is shown quantitatively that all the PMMA is present in subinclusion form. It is possible to manipulate the dispersed phase internal structure from small PMMA subinclusions dispersed in a larger PS particle to a PS/PMMA core−shell structure upon decreasing the PS/PMMA composition ratio. Coalescence of composite droplets was also investigated. Upon annealing, these systems clearly experience a dual coalescence process: composite droplet/composite droplet coalescence and coalescence between dispersed subinclusion particles. Alt...

Unconfined compression of articular cartilage: nonlinear behavior and comparison with a fibril-reinforced biphasic model.

Abstract: Mechanical behavior of articular cartilage was characterized in unconfined compression to delineate regimes of linear and nonlinear behavior, to investigate the ability of a fibril-reinforced biphasic model to describe measurements, and to test the prediction of biphasic and poroelastic models that tissue dimensions alter tissue stiffness through a specific scaling law for time and frequency. Disks of full-thickness adult articular cartilage from bovine humeral heads were subjected to successive applications of small-amplitude ramp compressions cumulating to a 10 percent compression offset where a series of sinusoidal and ramp compression and ramp release displacements were superposed. We found all equilibrium behavior (up to 10 percent axial compression offset) to be linear, while most nonequilibrium behavior was nonlinear, with the exception of small-amplitude ramp compressions applied from the same compression offset. Observed nonlinear behavior included compression-offset-dependent stiffening of the transient response to ramp compression, nonlinear maintenance of compressive stress during release from a prescribed offset, and a nonlinear reduction in dynamic stiffness with increasing amplitudes of sinusoidal compression. The fibril-reinforced biphasic model was able to describe stress relaxation response to ramp compression, including the high ratio of peak to equilibrium load. However, compression offset-dependent stiffening appeared to suggest strain-dependent parameters involving strain-dependent fibril network stiffness and strain-dependent hydraulic permeability. Finally, testing of disks of different diameters and rescaling of the frequency according to the rule prescribed by current biphasic and poroelastic models (rescaling with respect to the sample's radius squared) reasonably confirmed the validity of that scaling rule. The overall results of this study support several aspects of current theoretical models of articular cartilage mechanical behavior, motivate further experimental characterization, and suggest the inclusion of specific nonlinear behaviors to models.

A seismic-based cross-section of the Grenville Orogen in southern Ontario and western Quebec

Abstract: A schematic crustal cross-section is presented for the southwestern Grenville Province based on reprocessed Lithoprobe near-vertical incidence seismic reflection data and compiled seismic refractio...

Study of biodegradation behavior of chitosan-xanthan microspheres in simulated physiological media.

Abstract: Microspheres of a polyelectrolyte complex hydrogel were prepared from chitosan and xanthan after interaction between the two polyionic polymers. Their biodegradation was studied vs. chitosan. Simulated gastric fluid (SGF, pH 1.2) and intestinal fluid (SIF, pH 7.5) both as biodegradation media and phosphate buffered saline (PBS, pH 7.4) as a negative control were used. The degradation studies were performed at 37 degrees C at 240 rpm permanent stirring to mimic the physiologic conditions. High performance liquid chromatography (HPLC) was carried out to quantify the chitosan degradation products using glucosamine (GA) and N-acetyl-D-glucosamine (N-Ac-GA) as references. The peaks area integration method was used to determine the amount of each degradation product as a function of incubation time in the media. The effect of the media on the morphological structure of microspheres was assessed by scanning electron microscopy. From HPLC studies, it appeared that in SGF and SIF the major degradation products were glucosamine (GA) and N-acetyl-D-glucosamine (NAc-GA). In the first 15 days, oligochitosan fractions were released from the complex, whereas N-acetyl-D-glucosamine was detected in the media after this period. The degradation kinetics were assessed by the measurement of the cumulative degradation products, which showed faster degradation of chitosan than the complex in SGF and SIF. SEM micrographs showed an enhancement of microsphere porosity as a function of incubation time in the simulated physiological media. Our results suggest a better control of the degradation kinetics when chitosan is complexed to xanthan.

Optimization method for 3D bracing correction of scoliosis using a finite element model.

Abstract: Scoliosis is a complex three-dimensional deformity of the spine and rib cage frequently treated by brace. Although bracing produces significant correction in the frontal plane, it generally reduces the normal sagittal plane curvatures and has limited effect in the transverse plane. The goal of this study is to develop a new optimization approach using a finite element model of the spine and rib cage in order to find optimal correction patterns. The objective function to be minimized took account of coronal and sagittal offsets from a normal spine at the thoracic and lumbar apices as well as the rib hump. Two different optimization studies were performed using the finite element model, which was personalized to the geometry of 20 different scoliotic patients. The first study took into account only the thoracic deformity, while the second considered both the thoracic and lumbar deformities. The optimization produced an average of 56% and 51% reduction of the objective function respectively in the two studies. Optimal forces were mostly located on the convex side of the curve. This study demonstrates the feasibility of using an optimization approach with a finite element model of the trunk to analyze the biomechanics of bracing, and may be useful in the design of new and more effective braces.

On the choice of “Geometric” thermodynamic models

Abstract: A number of “geometric” models have been proposed for estimating the thermodynamic properties of a ternary solution from optimized data for its binary subsystems. Among the most common of these are the Kohler, Muggianu, Kohler/Toop, and Muggianu/Toop models. The latter two are “asymmetric” models in that one component is singled out and treated differently, whereas the first two models are “symmetric.” It is shown that the use of a symmetric model when an asymmetric model is more appropriate can often give rise to large errors. Equations are proposed for extending the symmetric/asymmetric dichotomy into N-component systems (N=3), while still permitting the flexibility to choose either a symmetric or an asymmetric model for any ternary subsystem. An improved general functional form for “ternary terms” in the excess Gibbs energy expression is also proposed. These terms are related to the effect of a third component upon the binary pair interaction energies. All the above considerations also apply when short-range ordering is taken into account by using the modified quasichemical model. Finally, some arguments in favor of the Kohler model over the Muggianu model are presented.

Implantable selective stimulator to improve bladder voiding: design and chronic experiments in dogs

Abstract: Among the treatments to enhance the bladder voiding, the sacral roots neurostimulation is one of the most promising techniques. The electrostimulation of sacral nerves provokes a simultaneous contraction of the detrusor muscle as well as the external urethral sphincter (EUS). A new simplified-architecture implantable stimulator with its wireless controller have been designed to investigate high-frequency inhibition stimulation strategies. This innovative technique based on high-frequency inhibition reduces sphincter activity during stimulation. Low-frequency current pulses also applied to the sacral roots induces contraction of the detrusor muscle resulting in low pressure voiding. Chronic experiments were carried out on ten male mongrel paraplegic dogs. One cuff electrode was implanted along with each stimulator for eight months. The animals were stimulated twice a day using the prototypes of the authors' implantable selective stimulator while voided and residual urine volume were measured during the procedure. These experiments revealed that the proposed stimulation strategy enhances bladder voiding by more than 50% in comparison with low-frequency only stimulation. The residual urine volume was reduced to an average of 9% and low pressure micturition was achieved as shown by weekly cystourethrogram.

Improvement of recombinant protein production with the human adenovirus/293S expression system using fed-batch strategies.

Abstract: The human adenovirus/293S cell expression system is used for the production of either recombinant protein or adenovirus vectors for use in gene therapy. In this work, the production of protein tyrosine phosphatase (PTP1C) was used as a model for the scale-up of both applications. Maximum specific production of 30 to 45 mug of active protein/10(6) cells was maintained upon infection with adenovirus vectors at cell densities between 2 x 10(6) to 3 x 10(6) cells/mL in a 3.5-L bioreactor. This was achieved by resuspending the culture in fresh medium at infection time. The pH was kept at 7.0 throughout the experiment and, at 24 h postinfection, glucose and essential amino acids were added. Attempts to replace the complete change of medium at the time of infection with nutrient supplementation of the used medium led to lower production levels, suggesting that protein expression was limited not by the absence of a key nutrient but by inhibitory factors. Two potentially inhibitory factors were investigated: lactic acid accumulation and increased osmolarity. Medium acidification such as that which would be brought about by lactic acid accumulation was shown to depress PTP1C production. The lactate molecule itself decreased the cell viability when added in concentrations of 20 mM or more. But the specific productivity was affected at higher lactate concentrations of 40 mM or more. Additions of glucose, amino acids, and NaHCO(3) used to control pH, led to increases in osmolarity. Osmolarities above 400 mOsm lowered cell density. However, specific production was not significantly affected below 500 mOsm. But, at 500 mOsm, PTP1C production peak was shifted from 48 to 72 hpi. Because of the cell loss, this per cell yield increase did not translate into higher volumetric production. When glucose concentrations was kept at 5 mM by fed-batch addition, lactate production and increases in osmolarity were reduced. In shake flasks, this method permitted maximum production with cells resuspended either in fresh or spent medium at infection. This fed-batch process was implemented successfully at the 3.5-L scale. Fed-batch with glucose may provide a means to increase infected-cell density beyond 3 x 10(6) cells/mL.

A Comparative Assessment of the Performance of the Kenics and SMX Static Mixers

Abstract: The performance of two commercial static mixers in the laminar creeping flow regime, the Kenics mixer (Chemineer) and the SMX mixer (Koch Engineering), are compared using 3D numerical simulations. Several criteria are chosen as the basis for the performance evaluation, namely, the pressure drop, the mixer length, the Lyapunov exponent, the mean shear rate and the intensity of segregation. It appears that the SMX mixer is more efficient than the Kenics mixer to achieve a difficult mixing task or when installation space is restricted.

293SF Metabolic Flux Analysis during Cell Growth and Infection with an Adenoviral Vector

Abstract: Metabolic flux quantification of cell culture is becoming a crucial means to improve cell growth as well as protein and vector productions. The technique allows rapid determination of cell culture status, thus providing a tool for further feeding improvements. Herein, we report on key results of a metabolic investigation using 293 cells adapted to suspension and serum-free medium (293SF) during growth and infection with an adenoviral vector encoding the green fluorescence protein (GFP). The model developed contains 35 fluxes, which include the main fluxes of glycolysis, glutaminolysis, and amino acids pathways. It requires specific consumption and production rate measurements of amino acids, glucose, lactate, NH(3), and O(2), as well as DNA and total proteins biosynthesis rate measurements. Also, it was found that extracellular protein concentration measurement is important for flux calculation accuracy. With this model, we are able to describe the 293SF cell metabolism, grown under different culture conditions in a 3-L controlled bioreactor for batch and fed-batch with low glucose. The metabolism is also investigated during infection under two different feeding strategies: a fed-batch starting at the end of the growth phase and extending during infection without medium change and a fed-batch after infection following medium renewal. Differences in metabolism are observed between growth and infection, as well as between the different feeding strategies, thus providing a better understanding of the general metabolism.

Electrical and optical diagnostics of dielectric barrier discharges (DBD) in He and N2 for polymer treatment

Abstract: Synchronous, real-time optical and electrical diagnostics have been carried out on dielectric barrier discharges in flowing gases (air, He, N2) at atmospheric pressure A true “Atmospheric Pressure Glow Discharge” (APGD) is observed in N2 when O2 and H2 concentrations are below ≈500 ppm and 2500 ppm,respectively, and the APGD regime can be beneficially modified by suitably chosen dielectric coatings X-ray photoelectron spectroscopy (XPS) analyses of some APGD-treated polymer surfaces are presented