Social actors and their role in metropolitan governance in Montréal: towards an inclusive coalition?

The article is about the role of civil society organizations in the governance of the Montréal metropolitan region. It identifies a high level of cooperation around metropolitan scale issues on the part of these organizations. In the Montréal region, government agencies as well as private corporations demonstrate readiness to work alongside civil society organizations on joint projects. Evidence of this type of collaboration is particularly strong in the case of economic development, neighbourhood revitalization and cultural initiatives. This form of cooperation is perceived as a manifestation of the so-called “Québec model” and is an asset for the Montréal metropolitan region. The article demonstrates that interventions that involve social organizations are more likely to be successful than those that turn their back on these organizations.     

Comparison between real‐time dynamic substructuring and shake table testing techniques for nonlinear seismic applications

Results from real‐time dynamic substructuring (RTDS) tests are compared with results from shake table tests performed on a two‐storey steel building structure model. At each storey, the structural system consists of a cantilevered steel column resisting lateral loads in bending. In two tests, a slender diagonal tension‐only steel bracing member was added at the first floor to obtain an unsymmetrical system with highly variable stiffness. Only the first‐storey structural components were included in the RTDS test program and a Rosenbrock‐W linearly implicit integration scheme was adopted for the numerical solution. The tests were performed under seismic ground motions exhibiting various amplitude levels and frequency contents to develop first and second mode‐dominated responses as well as elastic and inelastic responses. A chirp signal was also used. Coherent results were obtained between the shake table and the RTDS testing techniques, indicating that RTDS testing methods can be used to successfully reproduce both the linear and nonlinear seismic responses of ductile structural steel seismic force resisting systems. The time delay introduced by actuator‐control systems was also studied and a novel adaptive compensation scheme is proposed. Copyright © 2010 John Wiley & Sons, Ltd.     

Seismic retrofit of low‐rise steel buildings in Canada using rocking steel braced frames

This article examines the use of rocking steel braced frames for the retrofit of existing seismically deficient steel building structures. Rocking is also used to achieve superior seismic performance to reduce repair costs and disruption time after earthquakes. The study focuses on low‐rise buildings for which re‐centring is solely provided by gravity loads rather than added post‐tensioning elements. Friction energy dissipative (ED) devices are used to control drifts. The system is applied to 2‐storey and 3‐storey structures located in 2 seismically active regions of Canada. Firm ground and soft soil conditions are considered. The seismic performance of the retrofit scheme is evaluated using nonlinear dynamic analysis and ASCE 41‐13. For all structures, rocking permits to achieve immediate occupancy performance under 2% in 50 years seismic hazard if the braces and their connections at the building's top storeys are strengthened to resist amplified forces due to higher mode response. Base shears are also increased due to higher modes. Impact at column bases upon rocking induces magnified column forces and vertical response in the gravity system. Friction ED is found more effective for drift control than systems with ring springs or bars yielding in tension. Drifts are sufficiently small to achieve position retention performance for most nonstructural components. Horizontal accelerations are generally lower than predicted from ASCE 41 for regular nonrocking structures. Vertical accelerations in the gravity framing directly connected to the rocking frame are however higher than those predicted for ordinary structures. Vertical ground motions have limited effect on frame response.     

A Practical Approach to the Estimation of Amplitude and Time-Delay Parameters of a Composite Signal

A method for estimating the amplitude and time-delay parameters for signals that can be represented as a sum of a number of scaled and delayed replicas of a known signal in the presence of nonwhite Gaussian noise is presented. The method is based upon the principles of maximum likelihood (ML) estimation, but at certain key points simplifying assumptions are made that result in a computationally practical estimation scheme. The results are compared with other related results in the literature. Simulation results are presented which support the methods derived.     

Mechanisms to limit higher mode effects in a controlled rocking steel frame. 1: Concept,modelling, and low‐amplitude shake table testing

Controlled rocking steel frames have been proposed as an efficient way to avoid the structural damage and residual deformations that are expected in conventional seismic force resisting systems. Although the base rocking response is intended to limit the force demands, higher mode effects can amplify member design forces, reducing the viability of the system. This paper suggests that seismic forces may be limited more effectively by providing multiple force‐limiting mechanisms. Two techniques are proposed: detailing one or more rocking joints above the base rocking joint and providing a self‐centring energy dissipative (SCED) brace at one or more levels. These concepts are applied to the design of an eight‐storey prototype structure and a shake table model at 30% scale. A simple numerical model that was used as a design tool is in good agreement with frequency characterization and low‐amplitude seismic tests of the shake table model, particularly when multiple force‐limiting mechanisms are active. These results suggest that the proposed mechanisms can enable better capacity design by reducing the variability of peak seismic force demands without causing excessive displacements. Similar results are expected for other systems that rely on a single location of concentrated nonlinearity to limit peak seismic loads. Copyright © 2012 John Wiley & Sons, Ltd.     

Conceptual model of leachate migration in a granular aquifer derived from the integration of multi-source characterization data (St-Lambert,Canada)

Numerical models encompassing source zones and receptors, based on representative conceptual models and accounting for aquifer heterogeneity, are needed to understand contaminant migration and fate; however, aquifer characterization seldom provides the necessary data. This study aimed to develop a workflow for field characterization and data integration, which could: (1) be adapted to the definition of subwatershed-scale aquifer heterogeneity (over 10 km²) and (2) adequately support mass transport model development. The study involved the field investigation of a shallow granular aquifer in a 12-km² subwatershed in Saint-Lambert-de-Lauzon, Canada, in which a decommissioned landfill is emitting a leachate plume managed by natural attenuation. Using proven field methods, the characterization sequence was designed to optimize each method in terms of location, scale of acquisition, density and quality. The emphasis was on the acquisition of detailed indirect geophysical data that were integrated with direct hydraulic and geochemical data. This report focuses on the first qualitative and geostatistical data integration steps of the workflow leading to the development of a hydrogeological conceptual model. This is a prerequisite for further integration steps: prediction of hydrofacies and hydraulic conductivity (K), geostatistical simulations of K, studies of geochemical processes and numerical modeling.     

Current state and trends in Canadian Arctic marine ecosystems: I. Primary production

During the International Polar Year (IPY), large international research programs provided a unique opportunity for assessing the current state and trends in major components of arctic marine ecosystems at an exceptionally wide spatio-temporal scale: sampling covered most regions of the Canadian Arctic (IPY-Canada??s Three Oceans project), and the coastal and offshore areas of the southeastern Beaufort Sea were monitored over almost a full year (IPY-Circumpolar Flaw Lead project). The general goal of these projects was to improve our understanding of how the response of arctic marine ecosystems to climate warming will alter the productivity and structure of the food web and the ecosystem services it provides to Northerners. The present paper summarizes and discusses six key findings related to primary production (PP), which determines the amount of food available to consumers. (1) Offshore, the warming and freshening of the surface layer is leading to the displacement of large nanophytoplankton species by small picophytoplankton cells, with potentially profound bottom-up effects within the marine food web. (2) In coastal areas, PP increases as favourable winds and the deeper seaward retreat of ice promote upwelling. (3) Multiple upwelling events repeatedly provide food to herbivores throughout the growth season. (4) A substantial amount of pelagic PP occurs under thinning ice and cannot be detected by orbiting sensors. (5) Early PP in the spring does not imply a trophic mismatch with key herbivores. (6) The epipelagic ecosystem is very efficient at retaining carbon in surface waters and preventing its sedimentation to the benthos. While enhanced PP could result in increased fish and marine mammal harvests for Northerners, it will most likely be insufficient for sustainable large-scale commercial fisheries in the Canadian Arctic.     

Elemental and stable isotopic constraints on river influence and patterns of nitrogen cycling and biological productivity in Hudson Bay

Elemental (carbon and nitrogen) ratios and stable carbon and nitrogen isotope ratios (δ¹³C and δ¹⁵N) are examined in sediments and suspended particulate matter from Hudson Bay to study the influence of river inputs and autochthonous production on organic matter distribution. River-derived particulate organic matter (POM) is heterogeneous, nitrogen-poor and isotopically depleted, consistent with expectations for OM derived from terrestrial C3 vascular plant sources, and distinct from marine OM sources. Both δ¹³C and C/N source signatures seem to be transmitted to sediments with little or no modification, therefore making good tracers for terrigenous OM in Hudson Bay. They suggest progressively larger contributions from marine sources with distance from shore and secondarily from south to north, which broadly corresponds to the distribution of river inputs to Hudson Bay. Processes other than mixing of marine and terrigenous OM influence sedimentary δ¹⁵N values, including variability in the δ¹⁵N of phytoplankton in the Bay's surface waters due to differences in relative nitrate utilization, and post-production processes, which bring about an apparently constant ¹⁵N-enrichment between surface waters and underlying sediments. Variability in the δ¹⁵N of phytoplankton in the Bay's surface waters, in contrast, seems to be organized spatially with a pattern that suggests an inshore–offshore difference in surface water nitrogen conditions (open- vs. closed-system) and hence the δ¹⁵N value of phytoplankton. The δ¹⁵N patterns, supported by a simple nitrate box-model budget, suggest that in inshore regions of Hudson Bay, upwelling of deep, nutrient-rich waters replenishes surface nitrate, resulting in ‘open system’ conditions which tend to maintain nitrate δ¹⁵N at low and constant values, and these values are reflected in the sinking detritus. River inflow, which is constrained to inshore regions of Hudson Bay, appears to be a relatively minor source of nitrate compared to upwelling of deep waters. However, river inflow may contribute indirectly to enhanced inshore nutrient supply by supporting large-scale estuarine circulation and consequently entrainment and upwelling of deep water in this area. In contrast to previous proposals that Hudson Bay is oligotrophic because it receives too much fresh water (Dunbar, 1993), our results support most of the primary production being organized around the margin of the Bay, where river flow is constrained.     

Historical variability of subfossil chironomids (Diptera: Chironomidae) in three lakes impacted by natural and anthropogenic disturbances

In the eastern boreal forest of Quebec, Canada, harvesting strategies try to mimic the effects of fire on forest ecosystems, assuming that both disturbances have similar impacts. However impacts of both types of perturbations on lacustrine ecosystems, especially on chironomids (non-biting midges), are still poorly understood. The objectives of this study were to determine if logging and fire resulted in chironomid assemblages significantly different than pre-disturbance states and to see if the harvesting strategy (careful logging around advanced growth (CLAAG) and buffer zones) protect lakes from logging effects in the boreal forest. Three statistical tests were used to study the difference between pre- and post-disturbance assemblages: a principal component analysis (PCA), analysis of similarity (ANOSIM) and a non-metric multi-dimensional scaling (MDS) ordination. All statistical analyses suggested that fire did not have any effects on chironomid assemblages. The PCA analysis showed that two logging events in Lac aux Huards created chironomid assemblages slightly outside the pre-disturbance variability. However, ANOSIM showed that these differences were not significant at the 0.5% level of significance. These results suggest that the presence of a buffer zone probably limited the impacts of logging on lakes in this area.     

Kimberlitic sources of super-deep diamonds in the Juina area,Mato Grosso State,Brazil

The Juina diamond field, in the 1970–80s, was producing up to 5–6 million carats per year from rich placer deposits, but no economic primary deposits had been found in the area. In 2006–2007, Diagem Inc. discovered a group of diamondiferous kimberlitic pipes within the Chapadão Plateau (Chapadão, or Pandrea cluster), at the head of a drainage system which has produced most of the alluvial diamonds mined in the Juina area. Diamonds from placer deposits and newly discovered kimberlites are identical; they have super-deep origins from the upper-mantle and transition zone. Field observations and petrographic studies have identified crater-facies kimberlitic material at seven separate localities. Kimberlitic material is represented by tuffs, tuffisites and various epiclastic sediments containing chrome spinel, picroilmenite, manganoan ilmenite, zircon and diamond. The diamond grade varies from 0.2–1.8 ct/m³. Chrome spinel has 30–61 wt.% Cr₂O₃. Picroilmenite contains 6–14 wt.% MgO and 0.2–4 wt.% Cr₂O₃. Manganoan ilmenite has less than 3 wt.% MgO and 0.38–1.41 wt.% MnO. The ¹⁷⁶Hf/¹⁷⁷Hf ratio in kimberlitic zircons is 0.028288–0.28295 with ε_Hf = 5.9–8.3, and lies on the average kimberlite trend between depleted mantle and CHUR. The previously known barren and weakly diamondiferous kimberlites in the Juina area have ages of 79–80 Ma. In contrast, zircons from the newly discovered Chapadão kimberlites have a mean ²⁰⁶Pb/²³⁸U age of 93.6 ± 0.4 Ma, corresponding to a time of magmatic activity related to the opening of the southern part of the Atlantic Ocean. The most likely mechanism of the origin of kimberlitic magma is super-deep subduction process that initiated partial melting of zones in lower mantle with subsequent ascent of proto-kimberlitic magma.