Showing papers by "McGill University published in 1990"

Biosorption of Heavy Metals

Abstract: Only within the past decade has the potential of metal biosorption by biomass materials been well established. For economic reasons, of particular interest are abundant biomass types generated as a waste byproduct of large-scale industrial fermentations or certain metal-binding algae found in large quantities in the sea. These biomass types serve as a basis for newly developed metal biosorption processes foreseen particularly as a very competitive means for the detoxification of metal-bearing industrial effluents. The assessment of the metal-binding capacity of some new biosorbents is discussed. Lead and cadmium, for instance, have been effectively removed from very dilute solutions by the dried biomass of some ubiquitous species of brown marine algae such as Ascophyllum and Sargassum, which accumulate more than 30% of biomass dry weight in the metal. Mycelia of the industrial steroid-transforming fungi Rhizopus and Absidia are excellent biosorbents for lead, cadmium, copper, zinc, and uranium and also bind other heavy metals up to 25% of the biomass dry weight. Biosorption isotherm curves, derived from equilibrium batch sorption experiments, are used in the evaluation of metal uptake by different biosorbents. Further studies are focusing on the assessment of biosorbent performance in dynamic continuous-flow sorption systems. In the course of this work, new methodologies are being developed that are aimed at mathematical modeling of biosorption systems and their effective optimization. Elucidation of mechanisms active in metal biosorption is essential for successful exploitation of the phenomenon and for regeneration of biosorbent materials in multiple reuse cycles. The complex nature of biosorbent materials makes this task particularly challenging. Discussion focuses on the composition of marine algae polysaccharide structures, which seem instrumental in metal uptake and binding. The state of the art in the field of biosorption is reviewed in this article, with many references to recent reviews and key individual contributions.

Auditory Scene Analysis: The Perceptual Organization of Sound

Abstract: Auditory Scene Analysis addresses the problem of hearing complex auditory environments, using a series of creative analogies to describe the process required of the human auditory system as it analyzes mixtures of sounds to recover descriptions of individual sounds. In a unified and comprehensive way, Bregman establishes a theoretical framework that integrates his findings with an unusually wide range of previous research in psychoacoustics, speech perception, music theory and composition, and computer modeling.

On the control of automatic processes: A parallel distributed processing account of the stroop effect

Abstract: : A growing body of evidence suggests that traditional views of automaticity are in need of revision. For example, automaticity has often been treated as an all-or-none phenomenon, and traditional theories have held that automatic processes are independent of attention. Yet recent empirial data suggests that automatic processes are continuous, and furthermore are subject to attentional control. In this paper we present a model of attention which addresses these issues. Using a parallel distributed processing framework we propose that the attributes of automaticity depend upon the strength of a process and that strength increases with training. Using the Stroop effect as an example, we show how automatic processes are continuous and emerge gradually with practice. Specifically, we present a computational model of the Stroop task which simulates the time course of processing as well as the effects of learning.

Singularity analysis of closed-loop kinematic chains

Abstract: The different kinds of singularities encountered in closed-loop kinematics chains are analyzed. A general classification of these singularities in three main groups, which is based on the properties of the Jacobian matrices of the chain, is described. The identification of the singular configurations is particularly relevant for hard automation modules or robotic devices based on closed kinematic chains, such as linkages and parallel manipulators. Examples are given to illustrate the application of the method to these mechanical systems. >

The design school: Reconsidering the basic premises of strategic management

Abstract: Among the schools of thought on strategy formation, one in particular underlies almost all prescription in the field. Referred to as the ‘design school’, it proposes a simple model that views the process as one of design to achieve an essential fit between external threat and opportunity and internal distinctive competence. A number of premises underlie this model: that the process should be one of consciously controlled thought, specifically by the chief executive; that the model must be kept simple and informal; that the strategies produced should be unique, explicit, and simple; and that these strategies should appear fully formulated before they are implemented. This paper discusses and then critiques this model, focusing in particular on the problems of the conscious assessment of strengths and weaknesses, of the need to make strategies explicit, and of the separation between formulation and implementation. In so doing, it calls into question some of the most deep-seated beliefs in the field of strategic management, including its favorite method of pedagogy.

Malignant transformation by a eukaryotic initiation factor subunit that binds to mRNA 5' cap

Abstract: Eukaryotic cellular mRNAs have a 5' cap structure (m7 GpppX) that facilitates binding to ribosomes and is required for efficient translation. A specific initiation factor, eIF-4F, mediates the function of the cap and consists of three subunits, one of which, eIF-4E, binds the cap. This subunit is present in limiting amounts in the cell, and is thought to be regulated by phosphorylation: decreased phosphorylation of eIF-4E following various treatments correlates with a decrease in cellular translation rate. These observations suggest that eIF-4E lies on the mitogenic signal transduction pathway, and we reasoned that overexpression of eIF-4E might profoundly affect cellular growth properties. We report here that overexpression of eIF-4E in NIH 3T3 and Rat 2 fibroblasts causes their tumorigenic transformation as determined by three criteria: formation of transformed foci on a monolayer of cells; anchorage-independent growth; and tumour formation in nude mice.

Second Language Acquisition and Universal Grammar

Abstract: In this article, the motivation for Universal Grammar (UG), as assumed in the principles and parameters framework of generative grammar (Chomsky, 1981a, 1981b), is discussed, particular attention being paid to the logical problem of first language acquisition. The potential role of UG in second language (L2) acquisition is then considered. Three different positions are reviewed: (a) the claim that UG is not available to L2 learners; (b) the claim that UG is fully available; and (c) the claim that the L2 learner's access to UG is mediated by the mother tongue. This raises the issue of what kind of evidence can be used to decide between these three positions. Recent experimental research which argues for one or another of these positions by investigating the L2 status of the Subjacency Principle is reviewed, and the implications of this research are discussed.

Footprint prediction of scalar fluxes from analytical solutions of the diffusion equation

Abstract: The use of analytical solutions of the diffusion equation for ‘footprint prediction’ is explored. Quantitative information about the ‘footprint’, i.e., the upwind area most likely to affect a downwind flux measurement at a given height z, is essential when flux measurements from different platforms, particularly airborne ones, are compared. Analytical predictions are evaluated against numerical Lagrangian trajectory simulations which are detailed in a companion paper (Leclerc and Thurtell, 1990). For neutral stability, the structurally simple solutions proposed by Gash (1986) are shown to be capable of satisfactory approximation to numerical simulations over a wide range of heights, zero displacements and roughness lengths. Until more sophisticated practical solutions become available, it is suggested that apparent limitations in the validity of some assumptions underlying the Gash solutions for the case of very large surface roughness (forests) and tentative application of the solutions to cases of small thermal instability be dealt with by semi-empirical adjustment of the ratio of horizontal wind to friction velocity. An upper limit of validity of these solutions for z has yet to be established.

Responding to membership in a disadvantaged group : from acceptance to collective protest

Abstract: The question addressed is, when do disadvantaged-group members accept their situation, take individual action, or attempt to instigate collective action? Ss attempted to move from a low-status group into an advantaged, high-status group and were asked to respond to their subsequent rejec­ tion. Ss who believed that the high-status group was open to members of their group endorsed acceptance and individual actions. When access to the high-status group was restricted, even to the point of being almost closed (tokenism), Ss still preferred individual action. Disruptive forms of collective action were only favored by Ss who were told that the high-status group was completely closed to members oftheirgroup. Ss who believed they were near togainingentry into the high-sta­ tus group favored individual protest, while Ss distant from entry were more likely to accept their position. The theoretical and societal implications ofthese findings are discussed.

Focus-on-Form and Corrective Feedback in Communicative Language Teaching: Effects on Second Language Learning

Abstract: The developing oral English of approximately 100 second language learners (four intact classes) was examined in this study. The learners were native speakers of French (aged 10–12 years) who had received a 5-month intensive ESL course in either grade 5 or grade 6 in elementary schools in Quebec. A large corpus of classroom observation data was also analyzed. Substantial between-class differences were found in the accuracy with which students used such English structures as progressive -ing and adjective–noun order in noun phrases. There was some evidence that these differences (which were not correlated with performance on listening comprehension tests) were due to differences in teachers' form-focused instruction. These findings are discussed in terms of current competing views of the role of form-focused instruction in second language learning.

Local cerebral glucose metabolic rates in obsessive-compulsive disorder. Patients treated with clomipramine.

Abstract: • In a recent study, we reported abnormal local cerebral glucose metabolic rates in the orbital frontal cortex of patients with obsessive-compulsive disorder. Eight patients with obsessivecompulsive disorder scanned previously were scanned again during treatment with the tricyclic antidepressant clomipramine hydrochloride. Comparisons of local cerebral glucose metabolic rates for both groups showed a relative decrease in regions of the orbital frontal cortex and the left caudate, and an increase in other areas of the basal ganglia, including the right anterior putamen. When comparing patients who responded well to clomipramine with those who were either poor or partial responders, we found significant decreases only in the left caudate of patients who responded well to the drug. The present study suggests that clomipramine-induced improvement in obsessive-compulsive symptoms is associated with a return of regional brain metabolism to a more normal level in regions of the orbital frontal cortex and the caudate nucleus.

Bidirectional RNA helicase activity of eucaryotic translation initiation factors 4A and 4F.

Abstract: The mechanism of ribosome binding to eucaryotic mRNAs is not well understood, but it requires the participation of eucaryotic initiation factors eIF-4A, eIF-4B, and eIF-4F and the hydrolysis of ATP. Evidence has accumulated in support of a model in which these initiation factors function to unwind the 5'-proximal secondary structure in mRNA to facilitate ribosome binding. To obtain direct evidence for initiation factor-mediated RNA unwinding, we developed a simple assay to determine RNA helicase activity, and we show that eIF-4A or eIF-4F, in combination with eIF-4B, exhibits helicase activity. A striking and unprecedented feature of this activity is that it functions in a bidirectional manner. Thus, unwinding can occur either in the 5'-to-3' or 3'-to-5' direction. Unwinding in the 5'-to-3' direction by eIF-4F (the cap-binding protein complex), in conjunction with eIF-4B, was stimulated by the presence of the RNA 5' cap structure, whereas unwinding in the 3'-to-5' direction was completely cap independent. These results are discussed with respect to cap-dependent versus cap-independent mechanisms of ribosome binding to eucaryotic mRNAs.

A cache-based natural language model for speech recognition

Abstract: Speech-recognition systems must often decide between competing ways of breaking up the acoustic input into strings of words. Since the possible strings may be acoustically similar, a language model is required; given a word string, the model returns its linguistic probability. Several Markov language models are discussed. A novel kind of language model which reflects short-term patterns of word use by means of a cache component (analogous to cache memory in hardware terminology) is presented. The model also contains a 3g-gram component of the traditional type. The combined model and a pure 3g-gram model were tested on samples drawn from the Lancaster-Oslo/Bergen (LOB) corpus of English text. The relative performance of the two models is examined, and suggestions for the future improvements are made. >

Investigation of the laminate structure of lumbar disc anulus fibrosus.

Abstract: The structure of the lumbar disc anulus fibrosus was investigated using a layer-by-layer peeling technique and microscopic examination of various cut surfaces. Anulus specimens from spines of two different age groups and from two levels, L2–3 and L4–5, were examined. The vertebra-disc-vertebra units

Semantic memory loss in dementia of Alzheimer's type. What do various measures measure?

Abstract: This paper examines three methodological issues concerning the measurement of semantic memory impairment in brain-damaged patients. Ten carefully selected patients with dementia of Alzheimer's type (DAT) and anomia were studied. A battery of perceptual tests and direct tests of semantic memory led to the conclusion that these patients represented a homogeneous group having a prominent deterioration of their semantic memory store without visual perceptual deficits. The first issue addressed in this patient group was whether verbal fluency impairment accurately reflected the loss of semantic memory. It was found that verbal fluency (generation of semantic category lists) was impaired due to two major constraints: deterioration of semantic memory store, and variable difficulties in semantic search. Verbal fluency, therefore, reflects semantic memory loss to some degree, but is not a direct test of semantic memory store in DAT. The second issue was whether semantic memory impairment in our patients conformed to the 'semantic storage disorder' syndrome hypothesized by Shallice (1987). It was shown that, consistent with this hypothesis, the patients demonstrated co-occurrence of consistency of errors, loss of semantic cueing, and preserved superordinate knowledge with loss of detailed knowledge of concept items. The third issue was whether semantic cueing and semantic priming are altered in a similar manner in DAT. It demonstrated that semantic cueing and semantic priming, using the same words whose concepts were degraded in semantic memory, yielded an entirely different pattern of results. Cueing and priming therefore may not be used interchangeably in the study of semantic loss after brain damage.

Neurologic Sequelae of Domoic Acid Intoxication Due to the Ingestion of Contaminated Mussels

Abstract: In late 1987 there was an outbreak in Canada of gastrointestinal and neurologic symptoms after the consumption of mussels found to be contaminated with domoic acid, which is structurally related to the excitatory neurotransmitter glutamate. We studied the neurologic manifestations in 14 of the more severely affected patients and assessed the neuropathological findings in 4 others who died within four months of ingesting the mussels. In the acute phase of mussel-induced intoxication, the patients had headache, seizures, hemiparesis, ophthalmoplegia, and abnormalities of arousal ranging from agitation to coma. On neuropsychological testing several months later, 12 of the patients had severe anterograde-memory deficits, with relative preservation of other cognitive functions. Eleven patients had clinical and electromyographic evidence of pure motor or sensorimotor neuronopathy or axonopathy. Positron-emission tomography of four patients showed decreased glucose metabolism in the medial temporal lobes. Neuropathological studies in the four patients who died after mussel-induced intoxication demonstrated neuronal necrosis and loss, predominantly in the hippocampus and amygdala, in a pattern similar to that observed experimentally in animals after the administration of kainic acid, which is also structurally similar to glutamate and domoic acid. We conclude that intoxication with domoic acid causes a novel and distinct clinicopathologic syndrome characterized initially by widespread neurologic dysfunction and then by chronic residual memory deficits and motor neuronopathy or axonopathy.

Middle managers and strategy: Microdynamics of inclusion

Abstract: This paper examines the role of middle management in strategic processes in bureaucratic organizations; There is evidence of extensive dissatisfaction among mziddle managers, who often perceive that they are excluded from strategic processes. This exclusion is de-energizing, inefficient, and in the end, expensive. Although an elemlent of exclusion is probably inevitable, the extent to which it occurs varies across organizations. This suggests that both exclusion and its consequences can be alleviated. An application of microsociological theory to this problem focuses attention on discrete communnications about strategic generalities between superior and subordinate. This paper arglues that mziddle managers may either be excluded or included in such 'strategic conversations', but inclusion does not guarantee satisfaction. When included they nmay emerge energized or de-energized arolund strategic issues, depending on several important factors. Finally, the paper discusses the implications of these dynamics for more macro level processes, in particular, strategy as allocation of resources and strategy as interpretative schema. A set of propositions as to the likelihood of increasing or decreasing feelings of inclusion and motivation, and of sustaining such feelings over time, concludes this discussion.

Word-Recognition Skills of Adults with Childhood Diagnoses of Dyslexia.

Abstract: This study investigated whether the same pattern of reading deficits that characterize dyslexic children continue to characterize this population as it reaches adulthood.

System identification of human joint dynamics.

Abstract: The dynamics of joint mechanics are a fundamental characteristic of the motor system. They determine the displacements evoked by perturbing forces during postural control and the forces that must be generated to perform a voluntary movement. This article reviews experimental studies of these dynamics, with an emphasis on the behavior of single joints in alert humans. Technical aspects of the experimental and analytic methods that have been used are summarized first. Major results obtained with the different methods are then reviewed, compared, and contrasted. The interpretation of these results in terms of the underlying physiological mechanisms is then considered, with an emphasis on the relative contributions of passive properties of tissue, the mechanical behavior of muscle, and stretch reflexes. Finally, important unanswered questions regarding the dynamics of joint mechanics are reviewed.

The Personal/Group Discrimination Discrepancy Perceiving My Group, but not Myself, to be a Target for Discrimination

Abstract: An unexpected finding that has surfaced in research on discrimination is that respondents perceive a higher level of discrimination directed at their group as a whole than at themselves as individual members of that group. The present study directly tested this personal/group discrepancy by focusing on two groups of Canadian immigrants who have been the targets of much discrimination, Haitian and South Asian women. Respondents were questioned about their personal and group discrimination on four separate dimensions: race, culture, status as newcomers to Canada, and gender Strong support was found for the generality of the personal/group discrimination discrepancy. Three possible explanations for the discrepancy point to possible avenues for future research: the denial of personal discrimination, the exaggeration of group discrimination, and information-processing biases.

Hypothalamic-pituitary-adrenal activity in aged, cognitively impaired and cognitively unimpaired rats.

Abstract: There is a tendency for increased hypothalamic-pituitary-adrenal (HPA) activity with age in the rat, and the resulting elevations in circulating glucocorticoid levels have been implicated in the occurrence of hippocampal pathology and memory deficits. In the experiments reported here, we examined whether HPA dysfunction is selectively associated with cognitive impairments in a population of aged rats. Fifty-eight 23-27-month-old male Long-Evans rats were screened for spatial memory impairments using the Morris swim maze, and 2 groups of aged animals were selected; aged, cognitively impaired (AI) animals whose performance was significantly different (greater than 2 SD) from that of 6-month-old controls and aged, cognitively unimpaired (AU) animals whose performance was comparable to that of the young controls (a difference of less than 0.5 SD). Twenty-eight percent of the animals tested were designated as AI and 20% as AU. Histological analysis of a subset of these animals showed that, while both AU and AI animals showed neuron loss in the pyramidal cell fields of the hippocampus, the loss was significantly greater in the AI animals. The AI animals showed clear evidence of increased HPA activity. Thus, basal ACTH and corticosterone levels were significantly higher in the AI animals compared with both AU animals and young controls, especially during the dark phase of the cycle. The AI, AU, and young animals exhibited comparable corticosterone levels during a 20-min immobilization stress; however, following the termination of the stressor, corticosterone levels in AI animals were significantly elevated compared with both AU animals and controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Pain 'memories' in phantom limbs: review and clinical observations.

Abstract: This paper reviews reports of phantom limb sensations which resemble somatosensory events experienced in the limb before amputation. It also presents descriptions of this phenomenon in 68 amputees who took part in a series of clinical studies. These somatosensory memories are predominantly replicas of distressing pre-amputation lesions and pains which were experienced at or near the time of amputation, and are described as having the same qualities of sensation as the pre-amputation pain. The patients who experience these pains emphasize that they are suffering real pain which they can describe in vivid detail, and insist that the experience is not merely a cognitive recollection of an earlier pain. Reports of somatosensory memories are less common when there has been a discontinuity, or a pain-free interval, between the experience of pain and amputation. Among the somatosensory memories reported are cutaneous lesions, deep tissue injuries, bone and joint pain and painful pre-amputation postures. The experience of somatosensory memories does not appear to be related to the duration of pre-amputation pain, time since amputation, age, gender, prosthetic use, level of amputation, number of limbs amputated, or whether the amputation followed an accident or illness. The results suggest that somatosensory inputs of sufficient intensity and duration can produce lasting changes in central neural structures which combine with cognitive-evaluative memories of the pre-amputation pain to give rise to the unified experience of a past pain referred to the phantom limb. Implications for pre- and post-operative pain control are discussed.

Two members of the mouse mdr gene family confer multidrug resistance with overlapping but distinct drug specificities.

Abstract: We report the cloning and functional analysis of a complete clone for the third member of the mouse mdr gene family, mdr3. Nucleotide and predicted amino acid sequence analyses showed that the three mouse mdr genes encode highly homologous membrane glycoproteins, which share the same length (1,276 residues), the same predicted functional domains, and overall structural arrangement. Regions of divergence among the three proteins are concentrated in discrete segments of the predicted polypeptides. Sequence comparison indicated that the three mouse mdr genes were created from a common ancestor by two independent gene duplication events, the most recent one producing mdr1 and mdr3. When transfected and overexpressed in otherwise drug-sensitive cells, the mdr3 gene, like mdr1 and unlike mdr2, conferred multidrug resistance to these cells. In independently derived transfected cell clones expressing similar amounts of either MDR1 or MDR3 protein, the drug resistance profile conferred by mdr3 was distinct from that conferred by mdr1. Cells transfected with and expressing MDR1 showed a marked 7- to 10-fold preferential resistance to colchicine and Adriamycin compared with cells expressing equivalent amounts of MDR3. Conversely, cells transfected with and expressing MDR3 showed a two- to threefold preferential resistance to actinomycin D over their cellular counterpart expressing MDR1. These results suggest that MDR1 and MDR3 are membrane-associated efflux pumps which, in multidrug-resistant cells and perhaps normal tissues, have overlapping but distinct substrate specificities.