Showing papers by "Université du Québec à Montréal published in 2008"

Tracing the stepwise oxygenation of the Proterozoic ocean

Abstract: The oxygenation of the Earth's atmosphere is thought to have occurred in two steps near the beginning and the end of the Proterozoic eon, around 2,500 to 550 million years ago. The oxidation state of the ocean between these two steps and the timing of deep ocean oxygenation, however, remain poorly known. Scott et al. now use molybdenum and total organic carbon data from black shales to track the redox state of the ocean at this time. Molybdenum is an essential participant in nutrient cycling, and its availability is highly sensitive to Earth's redox state. The results provide a new narrative for the historical texture of Earth's oxygenation, and will be of relevance for the study of the events that presaged the appearance of animals on Earth. Molybdenum and total organic carbon data from black shales is used to gain insights into the redox state of the ocean. The data suggests mild oxidative weathering of the continents before ∼2,200 Myr ago, but weathering becomes more persistent and vigorous at ∼2,150 Myr ago, 200 million years after the initial rise in atmospheric oxygen. Limited availability of molybdenum after 1,800 Myr ago may have acted as a negative nutrient feedback limiting the spatial and temporal extent of sulphidic conditions. Biogeochemical signatures preserved in ancient sedimentary rocks provide clues to the nature and timing of the oxygenation of the Earth’s atmosphere. Geochemical data1,2,3,4,5,6 suggest that oxygenation proceeded in two broad steps near the beginning and end of the Proterozoic eon (2,500 to 542 million years ago). The oxidation state of the Proterozoic ocean between these two steps and the timing of deep-ocean oxygenation have important implications for the evolutionary course of life on Earth but remain poorly known. Here we present a new perspective on ocean oxygenation based on the authigenic accumulation of the redox-sensitive transition element molybdenum in sulphidic black shales. Accumulation of authigenic molybdenum from sea water is already seen in shales by 2,650 Myr ago; however, the small magnitudes of these enrichments reflect weak or transient7 sources of dissolved molybdenum before about 2,200 Myr ago, consistent with minimal oxidative weathering of the continents. Enrichments indicative of persistent and vigorous oxidative weathering appear in shales deposited at roughly 2,150 Myr ago, more than 200 million years after the initial rise in atmospheric oxygen1,2. Subsequent expansion of sulphidic conditions after about 1,800 Myr ago (refs 8, 9) maintained a mid-Proterozoic molybdenum reservoir below 20 per cent of the modern inventory, which in turn may have acted as a nutrient feedback limiting the spatiotemporal distribution of euxinic (sulphidic) bottom waters and perhaps the evolutionary and ecological expansion of eukaryotic organisms10. By 551 Myr ago, molybdenum contents reflect a greatly expanded oceanic reservoir due to oxygenation of the deep ocean and corresponding decrease in sulphidic conditions in the sediments and water column.

Climate-Driven Ecosystem Succession in the Sahara: The Past 6000 Years

Abstract: Desiccation of the Sahara since the middle Holocene has eradicated all but a few natural archives recording its transition from a "green Sahara" to the present hyperarid desert. Our continuous 6000- year paleoenvironmental reconstruction from northern Chad shows progressive drying of the regional terrestrial ecosystem in response to weakening insolation forcing of the African monsoon and abrupt hydrological change in the local aquatic ecosystem controlled by site- specific thresholds. Strong reductions in tropical trees and then Sahelian grassland cover allowed large- scale dust mobilization from 4300 calendar years before the present ( cal yr B. P.). Today's desert ecosystem and regional wind regime were established around 2700 cal yr B. P. This gradual rather than abrupt termination of the African Humid Period in the eastern Sahara suggests a relatively weak biogeophysical feedback on climate.

A Critique of Silviculture: Managing for Complexity

Abstract: New ideas in ecology have implications for managing forest ecosystems. The discipline of silviculture is at a crossroads. Silviculturists are under increasing pressure to develop practices that sustain the full function and dynamics of forested ecosystems and maintain ecosystem diversity and resilience while still providing needed wood products. "A Critique of Silviculture" offers a penetrating look at the current state of the field and provides suggestions for its future development.The book includes an overview of the historical developments of silvicultural techniques and describes how these developments are best understood in their contemporary philosophical, social, and ecological contexts. It also explains how the traditional strengths of silviculture are becoming limitations as society demands a varied set of benefits from forests and as we learn more about the importance of diversity on ecosystem functions and processes.The authors go on to explain how other fields, specifically ecology and complexity science, have developed in attempts to understand the diversity of nature and the variability and heterogeneity of ecosystems. The authors suggest that ideas and approaches from these fields could offer a road map to a new philosophical and practical approach that endorses managing forests as complex adaptive systems."A Critique of Silviculture" bridges a gap between silviculture and ecology that has long hindered the adoption of new ideas. It breaks the mold of disciplinary thinking by directly linking new ideas and findings in ecology and complexity science to the field of silviculture. This is a critically important book that is essential reading for anyone involved with forest ecology, forestry, silviculture, or the management of forested ecosystems.

Involvement of the low-density lipoprotein receptor-related protein in the transcytosis of the brain delivery vector angiopep-2.

Abstract: The blood-brain barrier (BBB) restricts the entry of proteins as well as potential drugs to cerebral tissues. We previously reported that a family of Kunitz domain-derived peptides called Angiopeps can be used as a drug delivery system for the brain. Here, we further characterize the transcytosis ability of these peptides using an in vitro model of the BBB and in situ brain perfusion. These peptides, and in particular Angiopep-2, exhibited higher transcytosis capacity and parenchymal accumulation than do transferrin, lactoferrin, and avidin. Angiopep-2 transport and accumulation in brain endothelial cells were unaffected by the P-glycoprotein inhibitor, cyclosporin A, indicating that this peptide is not a substrate for the efflux pump P-glycoprotein. However, competition studies show that activated alpha(2)-macroglobulin, a specific ligand for the low-density lipoprotein receptor-related protein-1 (LRP1) and Angiopep-2 can share the same receptor. In addition, LRP1 was detected in glioblastomas and brain metastases from lung and skin cancers. Fluorescent microscopy also revealed that Alexa488-Angiopep-2 co-localized with LRP1 in brain endothelial cell monolayers. Overall, these results suggest that Angiopep-2 transport across the BBB is, in part, mediated by LRP1.

Comparing alternative approaches to measuring the geographical accessibility of urban health services: Distance types and aggregation-error issues

Abstract: Over the past two decades, geographical accessibility of urban resources for population living in residential areas has received an increased focus in urban health studies. Operationalising and computing geographical accessibility measures depend on a set of four parameters, namely definition of residential areas, a method of aggregation, a measure of accessibility, and a type of distance. Yet, the choice of these parameters may potentially generate different results leading to significant measurement errors. The aim of this paper is to compare discrepancies in results for geographical accessibility of selected health care services for residential areas (i.e. census tracts) computed using different distance types and aggregation methods. First, the comparison of distance types demonstrates that Cartesian distances (Euclidean and Manhattan distances) are strongly correlated with more accurate network distances (shortest network and shortest network time distances) across the metropolitan area (Pearson correlation greater than 0.95). However, important local variations in correlation between Cartesian and network distances were observed notably in suburban areas where Cartesian distances were less precise. Second, the choice of the aggregation method is also important: in comparison to the most accurate aggregation method (population-weighted mean of the accessibility measure for census blocks within census tracts), accessibility measures computed from census tract centroids, though not inaccurate, yield important measurement errors for 5% to 10% of census tracts. Although errors associated to the choice of distance types and aggregation method are only important for about 10% of census tracts located mainly in suburban areas, we should not avoid using the best estimation method possible for evaluating geographical accessibility. This is especially so if these measures are to be included as a dimension of the built environment in studies investigating residential area effects on health. If these measures are not sufficiently precise, this could lead to errors or lack of precision in the estimation of residential area effects on health.

Sediment organic carbon burial in agriculturally eutrophic impoundments over the last century

Abstract: The OC buried in these lakes originates in both autochthonous and allochthonous production. These analyses suggest that OC sequestration in moderate to large impoundments may be double the rate assumed in previous analyses. Extrapolation suggests that they may bury 4 times as much carbon (C) as the world’s oceans. The world’s farm ponds alone may bury more OC than the oceans and 33% as much as the world’s rivers deliver to the sea.

The Cost of Pushing Pills: A New Estimate of Pharmaceutical Promotion Expenditures in the United States

Abstract: In the late 1950s, the late Democratic Senator Estes Kefauver, Chairman of the United States Senate's Anti-Trust and Monopoly Subcommittee, put together the first extensive indictment against the business workings of the pharmaceutical industry He laid three charges at the door of the industry: (1) Patents sustained predatory prices and excessive margins; (2) Costs and prices were extravagantly increased by large expenditures in marketing; and (3) Most of the industry's new products were no more effective than established drugs on the market [1] Kefauver's indictment against a marketing-driven industry created a representation of the pharmaceutical industry far different than the one offered by the industry itself As Froud and colleagues put it, the image of life-saving “researchers in white coats” was now contested by the one of greedy “reps in cars” [2] The outcome of the struggle over the image of the industry is crucial because of its potential to influence the regulatory environment in which the industry operates

Identification and Design of Peptides as a New Drug Delivery System for the Brain

Abstract: By controlling access to the brain, the blood-brain barrier (BBB) restricts the entry of proteins and potential drugs to cerebral tissues. We demonstrate here the transcytosis ability of aprotinin and peptides derived from Kunitz domains using an in vitro model of the BBB and in situ brain perfusion. Aprotinin transcytosis across bovine brain capillary endothelial cell (BBCEC) monolayers is at least 10-fold greater than that of holo-transferrin. Sucrose permeability was unaffected by high concentrations of aprotinin, indicating that transcytosis of aprotinin was unrelated to changes in the BBCEC monolayer integrity. Alignment of the amino acid sequence of aprotinin with the Kunitz domains of human proteins allowed the identification and design of a family of peptides, named Angiopeps. These peptides, and in particular Angiopep-2, exhibit higher transcytosis capacity and parenchyma accumulation than aprotinin. Overall, these results suggest that these Kunitz-derived peptides could be advantageously used as a new brain delivery system for pharmacological agents that do not readily enter the brain.

A Robust Variable Forgetting Factor Recursive Least-Squares Algorithm for System Identification

Abstract: The performance of the recursive least-squares (RLS) algorithm is governed by the forgetting factor. This parameter leads to a compromise between (1) the tracking capabilities and (2) the misadjustment and stability. In this letter, a variable forgetting factor RLS (VFF-RLS) algorithm is proposed for system identification. In general, the output of the unknown system is corrupted by a noise-like signal. This signal should be recovered in the error signal of the adaptive filter after this one converges to the true solution. This condition is used to control the value of the forgetting factor. The simulation results indicate the good performance and the robustness of the proposed algorithm.

The role of passion for teaching in intrapersonal and interpersonal outcomes

Abstract: The purpose of this study was to determine the role of passion in teachers' burnout symptoms, work satisfaction, and perceptions of positive student classroom behaviors. The dualistic model of passion (Vallerand et al., 2003) proposes 2 types of passion: harmonious and obsessive. In previous studies, harmonious passion has been shown to lead to adaptive outcomes (e.g., well-being and satisfaction), whereas obsessive passion has been shown to lead to less adaptive outcomes (e.g., shame and negative affect). In this study, 494 teachers completed measures of passion for teaching and various outcomes associated with the teaching profession twice over a 3-month period. Results of a cross-lag model based on structural equation modeling revealed that increases in harmonious passion for teaching predicted increases in work satisfaction and decreases in burnout symptoms over time, while changes in obsessive passion were unrelated to such outcomes. In addition, increases in both harmonious and obsessive passion predicted increases in teacher-perceived adaptive student behaviors over time. Overall, the results of the present study suggest that passion for teaching is an important concept to consider in education.

Reflections on self-determination theory

Abstract: Self-determination theory (SDT; Deci & Ryan, 2008) has led to much research over the past 25 years or so. The present collection of articles in this special issue attests to that. In this last article, we present a short overview of issues that cut across these papers as well as make recommendations for future research. We believe that the future is quite bright for SDT.

Child-Care Policy and the Labor Supply of Mothers with Young Children: A Natural Experiment from Canada

Abstract: In 1997, the provincial government of Quebec, the second most populous province in Canada, initiated a new child‐care policy. Licensed child‐care service providers began offering day‐care spaces at the reduced fee of $5.00 per day per child for children aged 4. By 2000, the policy applied to all children not in kindergarten. Using annual data (1993–2002) drawn from Statistics Canada's Survey of Labour and Income Dynamics, the results show that the policy had a large and statistically significant impact on the labor supply of mothers with preschool children.

Neodymium-142 Evidence for Hadean Mafic Crust

Abstract: Neodymium-142 data for rocks from the Nuvvuagittuq greenstone belt in northern Quebec, Canada, show that some rock types have lower 142Nd/144Nd ratios than the terrestrial standard (ϵ142Nd = –0.07 to –0.15). Within a mafic amphibolite unit, 142Nd/144Nd ratios correlate positively with Sm/Nd ratios and produce a 146Sm-142Nd isochron with an age of \(4280_{-81}^{+53}\) million years. These rocks thus sample incompatible-element-enriched material formed shortly after Earth formation and may represent the oldest preserved crustal section on Earth.

Joint development of bullying and victimization in adolescence: Relations to delinquency and self-harm.

Abstract: Objective: To estimate trajectories of bullying and victimization in early to mid-adolescence, associations between the trajectories, and links with delinquency and self-harm. Method: A total of 3,932 adolescents (50% boys) reported bullying (ages 14 to 16), victimization (ages 13 to 16), delinquency (age 16), and self-harm (age 16). Results: Two bullying trajectories (low/decreasing, high/increasing) and three victimization trajectories (low, high/decreasing, high/increasing) were identified. Over time, victimization increased the likelihood of involvement in bullying to a greater extent than bullying increased the likelihood of victimization. Boys and girls in the high/increasing bullying and the low or high/increasing victimization trajectories (i.e., the bullies and the bully-victims) were highest in mid-adolescent delinquency. Girls following the high/increasing bullying and high/increasing victimization trajectories (bully-victims) were the highest in mid-adolescent self-harm. Conclusions: Youths who are victimized by their peers are at increased risk, in turn, of victimizing others. Sex-specific adjustment problems are associated with differing patterns of involvement in bullying and victimization among adolescents. J. Am. Acad. Child Adolesc. Psychiatry, 2008;47(9):1030Y1038. Key Words: joint trajectories, bullying, victimization, delinquency, self-harm.

Personality, habitat use, and their consequences for survival in North American red squirrels Tamiasciurus hudsonicus

Abstract: Personality affects many aspects of an individual's behaviour, life history and fitness, and has been shown to be moderately heritable in wild populations. Correlations between personality and risk-taking that lead to life history tradeoffs could act to maintain variation in personality within a population, but this has not yet been tested. In this study, we used females from a marked population of North American red squirrels in Kluane, Yukon, to determine whether personality predicts risk-taking in the wild, and whether these risk-taking behaviours result in life history tradeoffs. We measured personality in open field and mirror image stimulation tests and extracted two traits, activity and aggressiveness, using principal component analysis and mixed model techniques. Using trapping records for individuals from February to September 2005, we obtained three measures of risk-taking: the number of trapping events, the number of different trapping locations, and the maximum distance between the home territory and a trapping event. We used GLMs to determine whether the activity and aggressiveness of individuals are related to these risk-taking behaviours, and found that active squirrels were trapped significantly more frequently and at a greater number of locations. There was also a significant interaction between activity and aggressiveness to affect the maximum capture distance. To determine if there are fitness tradeoffs associated with these risk-taking behaviours, we examined female bequeathal behaviour and survival. Bequeathing a territory increases offspring probability of overwinter survival, and we found that an increasing number of trapping locations was associated with an increasing tendency to bequeath. Active females were less likely to survive until the following spring. Risk-taking is therefore predicted by personality in this population, and they affect both survival and territorial bequeathal. These fitness tradeoffs may therefore lead to the maintenance of variation in personality.

Glycomimetics and Glycodendrimers as High Affinity Microbial Anti-adhesins

Abstract: Adhesion to epithelial surface is often the first step in bacterial and viral infection. In this process, the microbes use a variety of proteins for interaction with host carbohydrates presented as glycoconjugates on cell surfaces. Crystal structures of adhesin and lectin binding sites in complexes with oligosaccharide open the route for design and synthesis of glycomimetics, glycodendrimers, and glycopolymers that are able to block infection at an early stage.

Transfer effects in task-set cost and dual-task cost after dual-task training in older and younger adults : further evidence for cognitive plasticity in attentional control in late adulthood

Abstract: Older adults' difficulties in performing two tasks concurrently have been well documented (Kramer & Madden, 2008). It has been observed that the age-related differences in dual-task performance are larger when the two tasks require similar motor responses (2001) and that in some conditions older adults also show greater susceptibility than younger adults to input interference (Hein & Schubert, 2004). The authors recently observed that even when the two tasks require motor responses, both older and younger adults can learn to perform a visual discrimination task and an auditory discrimination task faster and more accurately (Bherer et al., 2005). In the present study, the authors extended this finding to a dual-task condition that involves two visual tasks requiring two motor responses. Older and younger adults completed a dual-task training program in which continuous individualized adaptive feedback was provided to enhance performance. The results indicate that, even with similar motor responses and two visual stimuli, both older and younger adults showed substantial gains in performance after training and that the improvement generalized to new task combinations involving new stimuli. These results suggest that dual-task skills can be substantially improved in older adults and that cognitive plasticity in attentional control is still possible in old age.

Natural Variability of Greenland Climate, Vegetation, and Ice Volume During the Past Million Years

Abstract: The response of the Greenland ice sheet to global warming is a source of concern notably because of its potential contribution to changes in the sea level. We demonstrated the natural vulnerability of the ice sheet by using pollen records from marine sediment off southwest Greenland that indicate important changes of the vegetation in Greenland over the past million years. The vegetation that developed over southern Greenland during the last interglacial period is consistent with model experiments, suggesting a reduced volume of the Greenland ice sheet. Abundant spruce pollen indicates that boreal coniferous forest developed some 400,000 years ago during the "warm" interval of marine isotope stage 11, providing a time frame for the development and decline of boreal ecosystems over a nearly ice-free Greenland.

Recent trends in glycodendrimer syntheses and applications.

Abstract: Carbohydrate protein interactions are at the front of several biological interactions spanning from cell growth and differentiation, cell signaling, apoptosis, cancer, and microbial infections. Classical medicinal glycochemistry has so far concentrated on designing glycosyl transferase and glycohydrolase inhibitors for which only handful candidates have emerged. Added to the complexity of drug resistances, drugs in development have rapidly witnessed this limitation as well. New approaches are therefore highly encouraged. Amongst these, blocking pathogen adhesions to host tissues as an early preventive mechanism is a foreseeable potentiality. It has the clear advantage that the pathogens are unlikely to mutate their anchoring motifs without upsetting their own binding to host tissues. An added dilemma is that these binding interactions are usually too weak to provide suitable drug candidates. As a consequence, the community has successfully come up with multivalent glycoconjugates having greatly enhanced avidity. An alternative strategy in which both monovalent ligands as well as the multivalent scaffolds undergoing QSAR improvement is thus suggested. This review will highlight recent trends toward the design of multivalent glycodendrimers and their biological applications.

Enabling the business strategy of SMEs through e‐business capabilities: A strategic alignment perspective

Abstract: Purpose – The present study aims at a deeper understanding of the performance outcomes of the alignment between the e‐business capabilities of manufacturing small‐ and medium‐sized enterprises (SMEs) and their business strategy in terms of Miles and Snow's recognised strategic typology that includes prospectors, analyzers, and defenders.Design/methodology/approach – From a contingency theory perspective, a survey of 107 Canadian manufacturers was used to collect data that were analyzed through correlation analysis.Findings – Results indicate that the ideal e‐business profiles vary in the relation to the firms' strategic orientation, whether it is of the defender, analyzer or prospector type. E‐business alignment has positive performance outcomes for manufacturing SMEs in terms of growth, productivity and financial performance.Research limitations/implications – The nature of the sample impose care in generalizing the results of the study. These results also allow us to emphasise the nature rather than the...

Challenging some tenets of Regional Climate Modelling

Abstract: Nested Regional Climate Models (RCMs) are increasingly used for climate-change projections in order to achieve spatial resolutions that would be computationally prohibitive with coupled global climate models. RCMs are commonly thought to behave as a sort of sophisticated magnifying glass to perform dynamical downscaling, which is to add fine-scale details upon the large-scale flow provided as time-dependent lateral boundary condition.