Showing papers by "Université de Montréal published in 1995"

Unit Root Tests in ARMA Models with Data-Dependent Methods for the Selection of the Truncation Lag

Abstract: We analyze the choice of the truncation lag in the context of the Said-Dickey test for the presence of a unit root in a general autoregressive moving average model. It is shown that a deterministic relationship between the truncation lag and the sample size is dominated by data-dependent rules that take sample information into account. In particular, we study data-dependent rules that are not constrained to satisfy the lower bound condition imposed by Said-Dickey. Akaike's information criterion falls into this category. The analytical properties of the truncation lag selected according to a class of information criteria are compared to those based on sequential testing for the significance of coefficients on additional lags. The asymptotic properties of the unit root test under various methods for selecting the truncation lag are analyzed, and simulations are used to show their distinctive behavior in finite samples. Our results favor methods based on sequential tests over those based on informat...

Toward a better definition of the restless legs syndrome

Abstract: A large International Restless Legs Syndrome (RLS) Study Group has been formed. As its first task, the group has taken upon itself the role of definig the clinical features of the RLS. As minimal criteria for diagnosis, the group proposes the following four features: (a) desire to move the extremities, often associated with paresthesias/dysesthesias; (b) motor restlessness; (c) worsening of symptoms at rest with at least temporary relief by activity, and (d) worsening of symptoms in the evening or night. Other features commonly seen in RLS include sleep disturbance, periodic limb movements in sleep and similar involuntary movements while awake, a normal neurological examination in the idiopathic from, a tendency for the symptoms to be worse in middle to older age, and, in some cases, a family history suggestive of an autosomal dominant mode of inheritance.

Probabilistic diversification and intensification in local search for vehicle routing

Abstract: This article presents a probabilistic technique to diversify, intensify, and parallelize a local search adapted for solving vehicle routing problems. This technique may be applied to a very wide variety of vehicle routing problems and local searches. It is shown that efficient first-level tabu searches for vehicle routing problems may be significantly improved with this technique. Moreover, the solutions produced by this technique may often be improved by a postoptimization technique presented in this article, too. The solutions of nearly forty problem instances of the literature have been improved.

Activated T cells induce interleukin-12 production by monocytes via CD40-CD40 ligand interaction

Abstract: Previous studies on the production of interleukin-12 (IL-12) have shown that it is released, together with other proinflammatory cytokines, shortly after exposure of phagocytic cells to a variety of pathogens. We here report that IL-12 is also released during the recall response to soluble antigen (Ag) devoid of intrinsic adjuvant activity. We show that activated T cells induce the production of IL-12 by monocytes via a mechanism involving the interaction of T cell-associated CD40 ligand with CD40 on monocytes. The data suggest that Ag presentation on monocytes favors the persistence of type 1 responses.

Versatile and efficient techniques for simulating cloth and other deformable objects

Abstract: We are presenting techniques for simulating the motion and the deformation of cloth, fabrics or, more generally, deformable surfaces. Our main goal is to be able to simulate any kind of surface without imposing restrictions on shape or geometrical environment. In particular, we are considering difficult situations with respect to deformations and collisions, like wrinkled fabric falling on the ground. Thus, we have enhanced existing algorithms in order to cope with any possible situation. A mechanical model has been implemented to deal with any irregular triangular meshes, handle high deformations despite rough discretisation, and cope with complex interacting collisions. Thus, it should deal efficiently with situations where nonlinearities and discontinuities are really non marginal. Collision detection has also been improved to efficiently detect self-collisions, and also to correctly consider collision orientations despite the lack of surface orientation information from preset geometrical contexts, using consistency checking and correction. We illustrate these features through simulation examples.

Arc Routing Problems, Part II: The Rural Postman Problem

Abstract: This is the second half of a two-part survey on arc routing problems. The first part appeared in the March-April 1995 issue of this journal. Here, the rural postman problem RPP is reviewed. The paper is organized as follows: applications, the undirected RPP, the directed RPP, the stacker crane problem, and the capacitated arc routing problem.

Hierarchical Recurrent Neural Networks for Long-Term Dependencies

Abstract: We have already shown that extracting long-term dependencies from sequential data is difficult, both for determimstic dynamical systems such as recurrent networks, and probabilistic models such as hidden Markov models (HMMs) or input/output hidden Markov models (IOHMMs). In practice, to avoid this problem, researchers have used domain specific a-priori knowledge to give meaning to the hidden or state variables representing past context. In this paper, we propose to use a more general type of a-priori knowledge, namely that the temporal dependencies are structured hierarchically. This implies that long-term dependencies are represented by variables with a long time scale. This principle is applied to a recurrent network which includes delays and multiple time scales. Experiments confirm the advantages of such structures. A similar approach is proposed for HMMs and IOHMMs.

An exchange heuristic for routeing problems with time windows

Abstract: In this paper, we compare different exchange heuristics for vehicle routeing problems with time windows. We also introduce a new 2-opt* exchange heuristic, and show that a hybrid approach, based on Or-opt and 2-opt* exchanges, is particularly powerful for problems with time windows. Computational results are reported for randomly generated problems and for a standard test set.

Distributed multimedia and QOS: a survey

Abstract: Quality of service (QOS) is increasingly important for all components within distributed multimedia systems, as this survey reveals. We discuss the QOS parameters found in communication protocols, operating systems, multimedia databases and file servers, as well as those directly affecting the human user. >

Arc Routing Problems, Part I: The Chinese Postman Problem

Abstract: Arc routing problems arise in several areas of distribution management and have long been the object of study by mathematicians and operations researchers. In the first of a two-part survey, the Chinese postman problem CPP is considered. The main algorithmic results for the CPP are reviewed in five main sections: the undirected CPP, the directed CPP, the windy postman problem, the mixed CPP, and the hierarchical CPP.

Archaean subduction inferred from seismic images of a mantle suture in the Superior Province

Abstract: PLATE tectonics provides the basis for the interpretation of most current terrestrial tectonic activity, and is widely accepted as having been active over much of the Earth's history1. Yet the timing of initiation of this process is subject to debate2–9. So far, the earliest seismic evidence for plate tectonics has come from a fossil mantle suture in the Svecofennian orogen (1.89 Gyr ago)10 and from inferred plate convergence, subduction and accretion in the Trans-Hudson orogen (1.91–1.79 Gyr ago)11. As yet, seismic data from Archaean areas have been able to demonstrate only the importance of compression in the construction of the continental crust12–15. Here we present seismic data from a collision zone in the Superior Province of Canada, involving the Abitibi granite–greenstone Subprovince and the plutonic, arc-related Opatica belt. We interpret dipping seismic reflections that extend 30km into the mantle as representing a relict 2.69-Gyr-old suture associated with subduction. Although crustal structure, lithospheric thicknesses and convergence rates may have differed from those seen today, these seismic data provide direct evidence that plate tectonics was active in late Archaean times, 800 Myr earlier than indicated by previous seismic reflection surveys.

Routing problems: A bibliography

Abstract: This bibliography contains 500 references on four classical routing problems: the Traveling Salesman Problem, the Vehicle Routing Problem, the Chinese Postman Problem, and the Rural Postman Problem. References are presented alphabetically under a number of subheadings.

The effects of background music on consumers' desire to affiliate in buyer‐seller interactions

Abstract: The effect of music-induced pleasure and arousal on consumers' desire to affiliate in buyer-seller interactions were investigated in the context of bank services. Background music was manipulated using classical music extracts pretested to vary in pleasure (low, moderate, and high) and arousal (low, moderate, and high) according to the Affect Grid (Russell, Weiss, & Mendelsohn, 1989). Independent and interactive effects of music-induced pleasure and arousal on consumers' desire to affiliate were found. Higher desire to affiliate was associated with more pleasure and more arousal; pleasure had a stronger positive impact under low and high arousal than under a moderate level, and arousal had a stronger effect under low and high pleasure compared to moderate level. Theoretical and practical implications of the results are provided. © 1995 John Wiley & Sons, Inc.

Deciding Not to GO: Neuronal Correlates of Response Selection in a GO/NOGO Task in Primate Premotor and Parietal Cortex

Abstract: Monkeys performed reaching movements in two opposite directions in a symmetrically rewarded GO/NOGO task with an instructed-delay period. Instructional cues were presented at the target locations. The decision not to move was clearly reflected in cell activity in dorsal premotor cortex, but not in parietal cortex area 5. In premotor cortex, the initial response (< 250 msec) of most cells to the appearance of the instructional cues in GO and NOGO trials was similar. However, by the end of the delay period, the responses of most cells were statistically different between the two trial types, and the population signals were much less directional in the NOGO trials than in the GO trials. In area 5, in contrast, single-cell and population signals were generally similar and strongly directional in both GO and NOGO trials. This result suggests a role for area 5 in visuomotor analysis for the guidance of limb movements. It further suggests that separate representations of potential motor responses to external inputs and of the intended response to that input can coexist in parietal and premotor cortex, respectively.

Normative Data for Grip Strength of Elderly Men and Women

Abstract: Objectives Grip strength is an important prerequisite for good performance of the upper limb, hence it is important to evaluate it correctly However, one of the main difficulties in evaluating the grip strength of elderly patients is the absence of valid norms Therefore, the objective of this study was to develop normative data for maximum grip strength of persons aged 60 years and older Method The grip strength of 360 subjects aged 60 years and older, randomly recruited by age and gender strata, was evaluated with the Jamar dynamometer and the Martin vigorimeter according to the protocol of the American Society of Hand Therapists Results Grip strength diminishes curvilinearly with age, and men are consistently stronger than women The data are presented by the means, standard deviations, and range, and as predictive equations obtained by regression analysis In addition to age and gender, hand circumference and body height proved to be the best indicators of grip strength for this population of elderly subjects Conclusion The random recruitment of subjects, the high participation rate in the study, and the comparability of the subjects who agreed to participate and those who refused give this study the high external validity that is essential to any norm study The predictive equations will help occupational therapists to better estimate the expected grip strength of elderly patients than they could if using only age and gender

Optical properties of rutile near its fundamental band gap.

Abstract: We report low-temperature absorption, time-integrated photoluminescence, and resonant-Raman-scattering spectra near the fundamental band gap of ${\mathrm{TiO}}_{2}$ single crystals. The photoluminescence spectrum comprises a first peak at \ensuremath{\Elzxh}\ensuremath{\omega}=3.031 eV, followed by several peaks at lower energies. A polarization study of the emission spectrum indicates that the highest energy peak corresponds to 2${\mathit{p}}_{\mathit{x}\mathit{y}}$ dipole-allowed second-class excitonic transitions while the lower-energy peaks are phonon replicas of the 1s quadrupolar exciton. This result is corroborated by time-resolved photoluminescence measurements. The near-band-gap optical response of ${\mathrm{TiO}}_{2}$ is thus controlled by two distinct exciton states. The Raman-scattering intensity is found to increase slowly for excitation energies in the range 2.7--3 eV. This indicates that the Raman cross-section enhancement is dominated by virtual transitions involving the first dipole-allowed direct gap at 4.2 eV.

Apoptosis in Target Organs of Hypertension

Abstract: Apoptosis or programmed cell death frequently parallels abnormalities in cell proliferation and differentiation. As hypertrophy/hyperplasia or remodeling occurs in organs affected by hypertension, we evaluated the degree of apoptosis in the heart, kidney, and brain in situ in genetically hypertensive mice and rats as well as in cultured vascular smooth muscle cells. Apoptosis was characterized by morphological features, DNA fragmentation, and laddering as well as by terminal deoxynucleotidyl transferase labeling of the 3' OH ends of both extracted DNA and tissue sections. The present report provides the first evidence of increased apoptosis in whole organs of genetically hypertensive rat and mouse strains: in the heart of spontaneously hypertensive rats (SHR) and in the heart (ventricular cardiomyocytes), kidney (inner cortex and medulla), and brain (cortex, striatum, hippocampus, and thalamus) of spontaneously hypertensive mice, with a higher effect of apoptotic inducers in cultured aortic smooth muscle cells derived from SHR. Both types of known apoptotic processes, oligonucleosomal cleavage and large DNA fragmentation, were observed in vascular smooth muscle cells, but only the former appeared to be increased in SHR. This study underlines the importance of cell death dysregulation in hypertension, reveals a new route for investigation of the pathogenesis of hypertension, and suggests novel targets of therapeutic intervention.

Overexpression of RNase H partially complements the growth defect of an Escherichia coli delta topA mutant: R-loop formation is a major problem in the absence of DNA topoisomerase I.

Abstract: Previous biochemical studies have suggested a role for bacterial DNA topoisomerase (TOPO) I in the suppression of R-loop formation during transcription In this report, we present several pieces of genetic evidence to support a model in which R-loop formation is dynamically regulated during transcription by activities of multiple DNA TOPOs and RNase H In addition, our results suggest that events leading to the serious growth problems in the absence of DNA TOPO I are linked to R-loop formation We show that the overexpression of RNase H, an enzyme that degrades the RNA moiety of an R loop, can partially compensate for the absence of DNA TOPO I We also note that a defect in DNA gyrase can correct several phenotypes associated with a mutation in the rnhA gene, which encodes the major RNase H activity In addition, we found that a combination of topA and rnhA mutations is lethal

A nuclear-encoded form II RuBisCO in dinoflagellates.

Abstract: The chloroplasts of most dinoflagellates are unusual in that they are surrounded by three membranes and contain the carotenoid peridinin. The ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO) in dinoflagellate chloroplasts was found here to also be unusual. Unlike other eukaryotes, dinoflagellates containing peridinin use a form of RuBisCO (form II) previously found only in some species of proteobacteria. Furthermore, this RuBisCO is not encoded in the chloroplast DNA, as is the case in other organisms, but is encoded by the nuclear DNA. The unusual nature of this enzyme and location of its gene support the idea that dinoflagellate chloroplasts may have had a distinctive evolutionary origin.