Showing papers by "Laval University published in 1991"

A Global Performance Index for the Kinematic Optimization of Robotic Manipulators

Abstract: In this paper, a novel performance index for the kinematic optimization of robotic manipulators is presented. The index is based on the condition number of the Jacobian matrix of the manipulator, which is known to be a measure of the amplification of the errors due to the kinematic and static transformations between the joint and Cartesian spaces. Moreover, the index proposed here, termed global conditioning index (CGI), is meant to assess the distribution of the aforementioned condition number over the whole workspace. Furthermore, the concept of a global index is applicable to other local kinematic or dynamic indices. The index introduced here is applied to a simple serial two-link manipulator, to a spherical three-degree-of-freedom serial wrist, and to three-degree-of-freedom parallel planar and spherical manipulators. Results of the optimization of these manipulators, based on the GCI, are included.

Catalytic palladium‐based membrane reactors: A review

Abstract: This paper is an extensive review of the literature dealing with the class of catalytic membrane reactors which involves hydrogen permeable membranes made of palladium and palladium alloys. The fundamental factors which affect hydrogen permeability are first discussed. A classification of the many reactions which have been conducted in such reactors at both laboratory and commercial scales is then presented. The various techniques for the preparation of palladium- based membranes are described and the literature on modeling and design of these reactors is also reviewed.

Chitosan Coating Effect on Storability and Quality of Fresh Strawberries

Abstract: The effect of chitosan coating (1.0 and 1.5% w/v) in controlling decay of strawberries at 13°C was investigated as compared to a fungicide, iprodione (Rovral®). Chitosan coating significantly reduced decay of berries (P ≤ 0.05) compared to the control. There was no significant difference between chitosan and fungicide treatments up to 21 days storage. Thereafter, Rovral®-treated berries decayed at a higher rate than chitosan-coated berries. Chitosan-coated berries stored at 4°C were firmer, higher in titratable acidity, and synthesized anthocyanin at a slower rate than Rovral®-treated or nontreated berries. Chitosan coating decreased respiration rate of the berries with a greater effect at higher concentration.

A Controlled Trial of Corticosteroid Injections into Facet Joints for Chronic Low Back Pain

Abstract: Background Chronic low back pain is a common problem with many treatments, few of which have been rigorously evaluated. This randomized, placebo-controlled trial was designed to evaluate the efficacy of injections of corticosteroid into facet joints to treat chronic low back pain. Methods Patients with chronic low back pain who reported immediate relief of their pain after injections of local anesthetic into the facet joints between the fourth and fifth lumbar vertebrae and the fifth lumbar and first sacral vertebrae were randomly assigned to receive under fluoroscopic guidance injections of either methylprednisolone acetate (20 mg; n = 49) or isotonic saline (n = 48) in the same facet joints. Ninety-five patients were followed for six months and their condition assessed with scales of pain severity, back mobility, and limitation of function. Results After one month, none of the outcome measures evaluating pain, functional status, and back flexion differed clinically or statistically between the ...

Network modulation of a slow intrinsic oscillation of cat thalamocortical neurons implicated in sleep delta waves : cortically induced synchronization and brainstem cholinergic suppression

Abstract: A slow (0.5-4 Hz) oscillation of thalamic neurons was recently described and attributed to the interplay of two intrinsic currents. In this study, we investigated the network modulation of this intrinsic thalamic oscillation within the frequency range of EEG sleep delta-waves. We performed intracellular and extracellular recordings of antidromically identified thalamocortical cells (n = 305) in sensory, motor, associational, and intralaminar nuclei of anesthetized cats. At the resting membrane potential, Vm (-60.3 +/- 0.4 mV, mean +/- SE), cortical stimulation induced spindle-like oscillations (7-14 Hz), whereas at Vm more negative than -65 mV the same stimuli triggered an oscillation within the EEG delta-frequency (0.5-4 Hz), consisting of low-threshold spikes (LTSs) followed by after hyperpolarizing potentials (AHPs). The LTS-AHP sequences outlasted cortical stimuli as a self-sustained rhythmicity at 1-2 Hz. Corticothalamic stimuli were able to transform subthreshold slow (0.5-4 Hz) oscillations, occurring spontaneously at Vm more negative than -65 mV, into rhythmic LTSs crowned by bursts of Na+ spikes that persisted for 10-20 sec after cessation of cortical volleys. Cortical volleys also revived a hyperpolarization-activated slow oscillation when it dampened after a few cycles. Auto- and crosscorrelograms of neuronal pairs revealed that unrelated cells became synchronized after a series of corticothalamic stimuli, with both neurons displaying rhythmic (1-2 Hz) bursts or spike trains. Since delta-thalamic oscillations, prevailing during late sleep stages, are triggered at more negative Vm than spindles characterizing the early sleep stage, we postulate a progressive hyperpolarization of thalamocortical neurons with the deepening of the behavioral state of EEG-synchronized sleep. In view of the evidence that cortical-elicited slow oscillations depend on synaptically induced hyperpolarization of thalamocortical cells, we propose that the potentiating influence of the corticothalamic input results from the engagement of two GABAergic thalamic cell classes, reticular and local-circuit neurons. The thalamocorticothalamic loop would transfer the spike bursts of thalamic oscillating cells to cortical targets, which in turn would reinforce the oscillation by direct pathways and/or indirect projections relayed by reticular and local-circuit thalamic cells. Stimulation of mesopontine cholinergic [peribrachial (PB) and laterodorsal tegmental (LDT)] nuclei in monoamine-depleted animals had an effect that was opposite to that exerted by corticothalamic volleys. PB/LDT stimulation reduced or suppressed the slow (1-4 Hz) oscillatory bursts of high-frequency spikes in thalamic cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Fast oscillations (20-40 Hz) in thalamocortical systems and their potentiation by mesopontine cholinergic nuclei in the cat.

Abstract: Previous investigations in various motor and sensory cortical areas have shown that fast oscillations (20-80 Hz) of focal electroencephalogram and multiunit activities occur spontaneously during increased alertness or are dependent upon optimal sensory stimuli. We now report the presence of 20- to 40-Hz rhythmic activities in intracellularly recorded thalamocortical cells of the cat. In some neurons, subthreshold oscillations were triggered by depolarizing pulses and eventually gave rise to action potentials. In other neurons, the oscillations consisted of fast prepotentials, occasionally generating full spikes that arose from the resting or even from hyperpolarized membrane potential levels, and leading to trains of spikes at more depolarized levels. The rhythmic nature of these fast prepotentials was confirmed by means of an autocorrelation study, which demonstrated clear peaks at 25-ms intervals (40 Hz). In view of the recent evidence that mesopontine cholinergic nuclei trigger and maintain activation processes in thalamocortical systems, we tested the possibility that stimulation of these brainstem nuclei potentiates the 40-Hz waves on the background of the cortical electroencephalogram. This was indeed the case. The potentiation outlasted the stimulation by 10-20 s. The brainstem-induced facilitation of cortical 40-Hz oscillations was blocked by scopolamine, a muscarinic antagonist. That this facilitation was transmitted by brainstem-thalamic cholinergic projections was confirmed by persistence of the phenomenon after large excitotoxic lesions of the nucleus basalis of Meynert.

Structure and Expression of a New Complementary DNA Encoding the almost Exclusive 3β-Hydroxysteroid Dehydrogenase/Δ5-Δ4-lsomerase in Human Adrenals and Gonads

Abstract: The 3β-hydroxysteroid dehydrogenase/Δ5-Δ4 isomerase (3βHSD) enzyme catalyzes the oxidation and isomerization of Δ5−3β-hydroxysteroid precursors into Δ4-ketosteroids, thus leading to the formation of all classes of steroid hormones. In addition, 3βHSD catalyzes the interconversion of 3β-hydroxy- and 3-keto-5α-androstane steroids. Clinical observations in patients with 3βHSD deficiency as well as our recent data obtained by Southern blot analysis using a human placental 3βHSD cDNA (type I) as probe suggested the existence of multiple related 3βHSD isoenzymes. We now report the isolation and characterization of a second type of cDNA clone (arbitrarily designated type II) encoding 3βHSD after screening of a human adrenal λgt22A library. The nucleotide sequence of 1676 basepairs of human 3βHSD type II cDNA predicts a protein of 371 amino acids with a calculated molecular mass of 41,921 daltons, which displays 93.5% and 96.2% homology with human placental type I and rhesus macaque ovary 3βHSD deduced proteins, ...

A Jinear formulation of the machine-part cell formation problem

Abstract: The machine-part group formation is an important issue in the design of cellular manufacturing systems. The present paper first discusses some of the alternative formulations of this problem, their advantages and disadvantages, and then suggests a new linear zero-one formulation which seems to have removed most of the disadvantages observed in other models. It will be shown that most of the integrality conditions of the proposed formulation can be relaxed. This considerably improves its computational feasibility and efficiency. Finally, a simulated annealing approach to deal with large-scale problems is also presented.

Postural Sway Characteristics of the Elderly Under Normal and Altered Visual and Support Surface Conditions

Abstract: One of the most pervasive findings in the literature on the aged is the general slowing of cognitive-motor responses with advancing age. Hence, an increased slowness in the processing of information from vestibular, visual, and somatosensory systems could contribute greatly to a decline in postural stability. To examine this question, in a cross-sectional investigation, postural sway behavior of elderly (n = 18) and young (n = 10) adults was examined under conditions that stressed the slower integrative mechanisms rather than the reflexive mechanisms of postural control. The postural sway behavior of young and elderly subjects was examined for a prolonged duration (80 s), under altered visual and/or support surface (5 cm thick foam surface) conditions, and contrasted with normal stance. Results showed that the exclusion or disruption of one of the sensory inputs, alone, was not consistently sufficient to differentiate between elderly and young adults, because of compensation by the remaining sensory sources. Both alterations together (i.e., visual and surface), however, had a substantially greater effect upon the elderly than the young.

Loss of abdominal fat and metabolic response to exercise training in obese women.

Abstract: Numerous studies have shown that a high accumulation of abdominal fat is associated with metabolic complications and with an increased risk of coronary heart disease. The present study examined the...

Risk theory for the compound Poisson process that is perturbed by diffusion

Abstract: The classical model of collective risk theory is extended in that a diffusion process is added to the compound Poisson process. It is shown that the probabilities of ruin (by oscillation or by a claim) satisfy certain defective renewal equations. The convolution formula for the probability of ruin is derived and interpreted in terms of the record highs of the aggregate loss process. If the distribution of the individual claim amounts are combinations of exponentials, the probabilities of ruin can be calculated in a transparent fashion. Finally, the role of the adjustment coefficient (for example, for the asymptotic formulas) is explained.

Beam propagation and the ABCD ray matrices.

Abstract: We have generalized the ABCD propagation law, Q(2) = (AQ(1) + B)/(CQ(1) + D), for an optical system by introducing a generalized complex radius of curvature Q for a general optical beam. The real part of 1/Q is related to the mean radius of curvature of the wave front, while the imaginary part is related to the second moment of the amplitude of the beam.

The Determinants of Country Risk Ratings

Abstract: The purpose of this paper is to replicate Euromoney's and Institutional Investor's country risk ratings on the basis of economic and political variables. The evidence reveals that country risk ratings respond to some of the variables suggested by the theory. In particular, both the level of per capita income and propensity to invest affect positively the rating of a country. In addition, high-ranking countries are less indebted than low-ranking countries. It also appears that the ability of the model to duplicate the two country risk measures is very similar and both magazines' ratings can be replicated to a significant degree with few available economic statistics.

Increased survival after treatments with anticancer agents of Chinese hamster cells expressing the human Mr 27,000 heat shock protein.

Abstract: A family of 10 thermoresistant cell lines cloned from Chinese hamster cells transfected with a plasmid containing the structural gene for the small human Mr 27,000 heat shock protein (HSP27) was used to assess the putative role of this heat shock protein in chemoresistance. These cells express varying amounts of human HSP27 in addition to the normal level of endogenous hamster HSP27. As previously observed in the case of thermoresistance, a significant positive linear correlation (P less than 0.05) was found between cell survival in response to doxorubicin and the total amount of HSP27 expressed. Some clones were also examined for resistance to other drugs and chemicals. A statistically significant increased survival relative to the parental cells was observed following treatment with daunorubicin (three clones studied), colchicine, vincristine, actinomycin D, hydrogen peroxide, and sodium arsenite (one clone studied). However, the clone which expressed the highest level of HSP27 was as sensitive as control cells to the cytotoxic action of bis-chloronitrosourea and 5-fluorouracil. The relationship between HSP27 overexpression and increased resistance to cytotoxic agents was also evaluated in three independent pooled cell populations stably transformed with both the human HSP27 and the xanthine-guanine phosphoribosyltransferase gene and selected on the basis of resistance to mycophenolic acid and aminopterin. The results indicated that these cells survived significantly better than the control cells transfected with the marker gene only when exposed to doxorubicin. HSP27-mediated cellular protection was not associated either with decreased drug accumulation or with overexpression of P-glycoprotein. It is suggested that HSP27 might be involved in some form of chemoresistance and could participate in the development of clinical resistance to antineoplastic drugs.

Phylogeographic structure in mitochondrial dna of the lake whitefish (coregonus clupeaformis) and its relation to pleistocene glaciations.

Abstract: Restriction-fragment length polymorphisms were employed to evaluate the phylogenetic relationships, the genetic diversity and the geographic structure in mitochondrial DNA (mtDNA) lineages of the lake whitefish, Coregonus clupeaformis. Thirteen restriction enzymes that produced 148 restriction fragments were used to assay mtDNAs of 525 specimens collected among 41 populations. The sampling covered the entire range of the species, from Alaska to Labrador. Four distinct phylogeographic assemblages were identified. The Beringian assemblage, confined to Yukon and Alaska, was phylogenetically distinct from other assemblages and exhibited the highest level of nucleotide diversity. The Acadian assemblage was confined to southeastern North America and composed of a unique mtDNA clade. The Atlantic assemblage was confined to southern Quebec and the northeastern United States and was also observed among anadromous populations of northern Hudson Bay. This group was highly polymorphic and responsible for most of the mtDNA diversity observed outside Beringia. The Mississippian assemblage occupied most of the actual range of lake whitefish, from the Mackenzie delta to Labrador. Ninety-two percent of all whitefish of this proposed origin belonged to a single mtDNA haplotype. Overall, the diversity, the geographic structure and the times of divergence of mtDNA phylogenetic assemblages correlate with the Pleistocene glaciations classically assumed to have dramatically altered the genetic diversity of northern fishes in recent evolutionary times. Our results emphasize the dominant role of these catastrophic events in shaping the population genetic structure of lake whitefish.

Error analysis of mixed-interpolated elements for reissner-mindlin plates

Abstract: We give an error analysis for the recently introduced mixed-interpolated finite element methods for Reissner-Mindlin plates. Optimal error estimates, which are valid uniformly with respect to the thickness of the plate, are proven for the deflection, rotation and the shear force. In addition, the earlier families are augmented with a new method with linear approximations for the deflection and the rotation. We also introduce a simple postprocessing method by which an improved approximation for the deflection can be obtained.

Detection and activity of a bacteriocin produced by Leuconostoc mesenteroides.

Abstract: Leuconostoc mesenteroides UL5 was found to produce a bacteriocin, referred as mesenterocin 5, active against Listeria monocytogenes strains but with no effect on several useful lactic acid bacteria. The antimicrobial substance is a protein, since its activity was completely destroyed following protease (pronase) treatment. However, it was relatively heat stable (100 degrees C for 30 min) and partially denaturated by chloroform. The inhibitory effect of the bacteriocin on sensitive bacterial strains was determined by a critical-dilution micromethod. Mutants of L. mesenteroides UL5 which had lost the capacity to produce the bacteriocin were obtained. The mutant strain was stable and phenotypically identical to parental cells and remained resistant to the bacteriocin. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis was used to detect bacteriocin activity corresponding to an apparent molecular mass of about 4.5 kDa. Images

USE of CHITOSAN COATING to REDUCE WATER LOSS and MAINTAIN QUALITY of CUCUMBER and BELL PEPPER FRUITS

Abstract: The effect of chitosan coating (1.0 and 1.5% w/v) on the storability of bell pepper and cucumber fruits stored at 13 and 20C (RH 85%) was determined by monitoring the weight loss, respiration and quality: Chitosan coating markedly reduced the weight loss in both bell pepper and cucumber at both temperatures. Increasing the concentration of chitosan from 1.0 to 1.5% (w/v) resulted in a significantly greater weight retention in both fruits. In addition, coating cucumber and bell pepper with chitosan reduced the respiration rate, loss of color, wilting and fungal infection. the mechanism by which chitosan coating delayed senescence in bell pepper and cucumber is most likely due to its ability to alleviate water stress.

A Modelling Framework for Integrating Layout Design and flow Network Design

Abstract: This chapter introduces a comprehensive modelling framework for integrating layout design and material flow network design toward the direct generation of net layouts including the design of the physical aisle system. Eight models are developed, each being specialized to deal with various facets of this integrated design. The framework offers an alternative conceptual platform to the Quadratic Assignment Problem for layout design researchers.

A computer-vision technique for the acquisition and processing of 3-D profiles of dental imprints: an application in orthodontics

Abstract: The authors present a computer vision technique for the acquisition and processing of 3-D images of the profile of wax dental imprints in the automation of diagnosis in orthodontics. The acquisition of the 3-D images is based on the absorption of light by a dispersive medium and uses standard CCD (charge coupled device) cameras. The profiles of both sides of the imprint are acquired simultaneously. The 3-D image of each side of the imprint is segmented by nonlinear filtering of the 3-D data, and the interstices between the teeth are detected. Two operators are presented: one for the detection of the interstices between the teeth for incisors, canines, and premolars, and one for those between molars. A method for deciding the optimal neighborhood of application of each operator is also presented. Experimental results show that the two operators are very effective at detecting the interstices. >

Visceral perception in health and functional dyspepsia : crossover study of gastric distension with placebo and domperidone

Abstract: The symptoms of functional dyspepsia are still unexplained. To evaluate the possible role of abnormal visceral perception, we studied the symptomatic responses and the pressure variations during progressive gastric distension in 10 female healthy control subjects (mean age 33.6 years) and in 10 female patients with functional dyspepsia (mean age 35.2 years). A rubber balloon was positioned 4 cm below the lower esophageal sphincter (LES) and inflated with progressively larger volumes of air by steps of 50 ml; pressures at the gastric fundus and at the LES were continuously recorded by perfused manometric catheters. Each subject was studied on two separate occasions after randomized double-blind administration of either placebo or 20 mg of domperidone. Symptomatic responses and the manometric data were analyzed at the time of the initial recognition of distension (bloating step) and at the time of reporting pain or up to a maximum of 700 ml of balloon inflation (pain or 700-ml step). On placebo, the volumes of gastric distension were more than two times lower in patients than in control subjects at the bloating step (185±32 ml vs 470±40 ml,P=0.001) and at the pain or 700-ml step (265±54 ml vs 600±34 ml,P<0.005), while the pressure gradients (pressure at inflation steps minus baseline pressure before beginning inflation) were not statistically different between the two groups. On domperidone, the volumes at each of the two steps did not change in comparison to results on placebo except in healthy controls at the bloating step (470±40 ml on placebo vs 355±35 ml on domperidone,P<0.001); however, there was a trend for pressure gradients to increase on domperidone in comparison to results on placebo. We conclude that patients with functional dyspepsia have a lower threshold both to the initial symptomatic recognition and to perception of pain during gastric distension and that domperidone might have an effect on the threshold of these conscious visceral sensations. This increased visceral perception may alone or with other abnormalities of the gastroduodenal tract explain the symptoms of functional dyspepsia.